Wheat Susceptibility Genes TaCAMTA2 and TaCAMTA3 Negatively Regulate Post-Penetration Resistance against Blumeria graminis forma specialis tritici

Blumeria graminis forma specialis tritici (B.g. tritici) is the airborne fungal pathogen that causes powdery mildew disease on hexaploid bread wheat. Calmodulin-binding transcription activators (CAMTAs) regulate plant responses to environments, but their potential functions in the regulation of wheat–B.g. tritici interaction remain unknown. In this study, the wheat CAMTA transcription factors TaCAMTA2 and TaCAMTA3 were identified as suppressors of wheat post-penetration resistance against powdery mildew. Transient overexpression of TaCAMTA2 and TaCAMTA3 enhanced the post-penetration susceptibility of wheat to B.g. tritici, while knockdown of TaCAMTA2 and TaCAMTA3 expression using transient- or virus-induced gene silencing compromised wheat post-penetration susceptibility to B.g. tritici. In addition, TaSARD1 and TaEDS1 were characterized as positive regulators of wheat post-penetration resistance against powdery mildew. Overexpressing TaSARD1 and TaEDS1 confers wheat post-penetration resistance against B.g. tritici, while silencing TaSARD1 and TaEDS1 enhances wheat post-penetration susceptibility to B.g. tritici. Importantly, we showed that expressions of TaSARD1 and TaEDS1 were potentiated by silencing of TaCAMTA2 and TaCAMTA3. Collectively, these results implicated that the Susceptibility genes TaCAMTA2 and TaCAMTA3 contribute to the wheat–B.g. tritici compatibility might via negative regulation of TaSARD1 and TaEDS1 expression.


Introduction
As one of the most widely grown small-grain cereal crops, bread wheat (Triticum aestivum L.) has served as a major staple food for thousands of years and provided about 20% of the calories consumed by humans [1]. With the increase in the global population, the demand for wheat grains is rapidly growing [1]. However, wheat production is seriously threatened by attacks from adapted pathogens and pests [2]. Powdery mildew is a devastating disease of wheat that is caused by the obligate biotrophic fungal pathogen Blumeria graminis forma specialis tritici (B.g. tritici), leading to 5-50% yield losses [3,4]. To date, the safest, most economical, and most effective strategy to control this epidemic is breeding B.g. tritici-resistant wheat cultivars [3,4]. Therefore, it is critical to elucidate the molecular interaction between wheat and B.g. tritici and identify key regulators of wheat resistance against powdery mildew disease.
In this research, two CAMTA transcription factor genes, TaCAMTA2 and TaCAMTA3, were characterized as Susceptibility (S) genes contributing to wheat-B.g. tritici compatibility. Transient overexpression of TaCAMTA2 and TaCAMTA3 resulted in enhanced wheat post-penetration susceptibility to B.g. tritici, while transient silencing of TaCAMTA2 and TaCAMTA3 led to attenuated wheat post-penetration susceptibility to B.g. tritici. Furthermore, overexpressing TaSARD1 and TaEDS1 could confer wheat post-penetration resistance against powdery mildew, while silencing TaSARD1 and TaEDS1 enhanced wheat post-penetration susceptibility to B.g. tritici. Moreover, TaCAMTA2 and TaCAMTA3 were demonstrated to negatively regulate the expression of the defense genes TaSARD1 and TaEDS1. These results strongly support that S genes TaCAMTA2 and TaCAMTA3 partially redundantly suppress wheat post-penetration resistance against B.g. tritici presumably via the negative regulation of expressions of defense genes TaSARD1 and TaEDS1.

Homology-Based Identification of TaCAMAT2 and TaCAMTA3 in Bread Wheat
Previous studies revealed that the Arabidopsis CAMTA transcription factor AtCAMTA3 plays a vital role in the regulation of plant immunity [29][30][31][32]. In this study, we are interested in exploring the function of the wheat homolog of AtCAMTA3 in the wheat-B.g. tritici interaction. To this end, we first searched the reference genome of the hexaploid bread wheat by using the amino acid sequence of Arabidopsis AtCAMTA3 (At2g22300) as a query and obtained TaCAMAT2 and TaCAMTA3, the most closely related homologs of AtCAMTA3, in bread wheat. Three highly homologous sequences of TaCAMAT2 genes separately located on chromosomes 4A, 4B, and 4D were obtained from the genome sequence of the hexaploid wheat and designated as TaCAMTA2-4A (TraesCS4A02G407100), TaCAMTA2-4B (TraesCS4B02G306300), and TaCAMTA2-4D (TraesCS4D02G304500). Similarly, three highly homologous sequences of TaCAMAT3 genes separately located on chromosomes 2A, 2B, and 2D were obtained from the genome sequence of the hexaploid wheat and designated as TaCAMTA3-2A (TraesCS2A02G163000), TaCAMTA3-2B (TraesCS2B02G188800), and TaCAMTA3-2D (TraesCS2D02G169900).

TaCAMAT2 and TaCAMTA3 Contribute to the Wheat Susceptibility to B.g. tritici
To study the function of TaCAMAT2 and TaCAMTA3 in the wheat-B.g. tritici interaction, we first employed transient gene expression assays to overexpress these TaCAMTA2-4A, TaCAMTA2-4B, TaCAMTA2-4D, TaCAMTA3-2A, TaCAMTA3-2B, or TaCAMTA3-2D genes in the leaf epidermal cells of the B.g. tritici-susceptible wheat cultivar Yannong 999. After inoculation of conidia from the virulent B.g. tritici isolate E09, the formation of fungal haustoria in the transformed wheat cells was statistically analyzed. As shown in Figure  2A, the B.g. tritici haustorium index (HI%) increased from 56% for the empty vector (OE-EV) control to above 70% on wheat cells overexpressing TaCAMTA2 or TaCAMTA3 genes. These results suggested that overexpression of TaCAMAT2 and TaCAMTA3 could significantly enhance wheat post-penetration susceptibility to B.g. tritici.
To further verify the function of TaCAMAT2 and TaCAMTA3 in the regulation of wheat-B.g. tritici interaction, we employed transiently induced gene silencing (TIGS) assays to silence all endogenous TaCAMAT2 or TaCAMTA3 genes in the epidermal cell of

TaCAMAT2 and TaCAMTA3
Contribute to the Wheat Susceptibility to B.g. tritici To study the function of TaCAMAT2 and TaCAMTA3 in the wheat-B.g. tritici interaction, we first employed transient gene expression assays to overexpress these TaCAMTA2-4A, TaCAMTA2-4B, TaCAMTA2-4D, TaCAMTA3-2A, TaCAMTA3-2B, or TaCAMTA3-2D genes in the leaf epidermal cells of the B.g. tritici-susceptible wheat cultivar Yannong 999. After inoculation of conidia from the virulent B.g. tritici isolate E09, the formation of fungal haustoria in the transformed wheat cells was statistically analyzed. As shown in Figure 2A, the B.g. tritici haustorium index (HI%) increased from 56% for the empty vector (OE-EV) control to above 70% on wheat cells overexpressing TaCAMTA2 or TaCAMTA3 genes. These results suggested that overexpression of TaCAMAT2 and TaCAMTA3 could significantly enhance wheat post-penetration susceptibility to B.g. tritici.
the virulent B.g. tritici isolate E09, the frequency of fungal haustorium formation in the transformed plant cells was scored. As shown in Figure 2B, the silencing of TaCAMAT2 or TaCAMTA3 genes resulted in a marked HI% decrease to about 27%, compared to 33% for empty vector (EV) controls. Significantly, simultaneous silencing of TaCAMAT2 and TaC-AMTA3 could lead to a further decrease in HI% to approximately 13%, suggesting that TaCAMTA2 and TaCAMTA3 might partially redundantly suppress post-penetration resistance of wheat to B.g. tritici.   TaCAMTA2 (BSMV-TaCAMTA2as), TaCAMTA3 (BSMV-TaCAMTA3as), or co-silencing TaCAMTA2 and TaCAMTA3 (BSMV-TaCAMTA2as + BSMV-TaCAMTA3as). At least 1000 wheat-B.g. tritici interaction sites were counted in one experiment for each treatment. For (A-D), three independent biological replicates were statistically analyzed for each treatment (t-test; * p < 0.05, ** p < 0.01).
To further verify the function of TaCAMAT2 and TaCAMTA3 in the regulation of wheat-B.g. tritici interaction, we employed transiently induced gene silencing (TIGS) assays to silence all endogenous TaCAMAT2 or TaCAMTA3 genes in the epidermal cell of the B.g. tritici-susceptible wheat cultivar Yannong 999. After inoculation of conidia from the virulent B.g. tritici isolate E09, the frequency of fungal haustorium formation in the transformed plant cells was scored. As shown in Figure 2B, the silencing of TaCAMAT2 or TaCAMTA3 genes resulted in a marked HI% decrease to about 27%, compared to 33% for empty vector (EV) controls. Significantly, simultaneous silencing of TaCAMAT2 and TaCAMTA3 could lead to a further decrease in HI% to approximately 13%, suggesting that TaCAMTA2 and TaCAMTA3 might partially redundantly suppress post-penetration resistance of wheat to B.g. tritici.
In addition, we performed barley stripe mosaic virus (BSMV)-induced gene silencing (BSMV-VIGS) to silence all endogenous TaCAMAT2 or TaCAMTA3 genes in the leaves of the B.g. tritici-susceptible wheat cultivar Yannong 999. qRT-PCR showed that the endogenous transcript level of TaCAMAT2 or TaCAMTA3 was substantially reduced in the indicated VIGS plants ( Figure 2C). Thereafter, these VIGS plants were inoculated with conidia from the virulent B.g. tritici isolate E09, and the formation of microcolonies was analyzed to evaluate the wheat's susceptibility to powdery mildew. B.g. tritici microcolony index (MI%) declined to approximate 40% on BSMV-TaCAMTA2as plants and 47% on BSMV-TaCAMTA3as plants, compared with 55% for the BSMV-γ plants ( Figure 2D). Notably, simultaneous silencing of TaCAMAT2 and TaCAMTA3 could lead to a further MI% decrease to about 28%. These data clearly indicate that TaCAMAT2 and TaCAMTA3 partially redundantly contribute to the wheat susceptibility to B.g. tritici.

TaSARD1 and TaEDS1 Positively Contribute to the Wheat Post-Penetration Resistance to B.g. tritici
To characterize the function of TaSARD1 and TaEDS1 in the wheat-B.g. tritici interaction, we first employed transient gene expression assays to overexpress TaSARD1.1-6A, or TaEDS1-5D genes in the leaf epidermal cell of the B.g. tritici-susceptible wheat cultivar Yannong 999. As shown in Figure 4A, the B.g. tritici HI% decreased from 54% for the empty vector control to less than 41% on wheat cells overexpressing TaSARD1 or TaEDS1 genes. These results suggested that overexpression of TaSARD1 or TaEDS1 remarkably attenuated wheat post-penetration susceptibility to B.g. tritici.
To further examine the function of TaSARD1 and TaEDS1 in regulating wheat-B.g. tritici interaction, we employed the TIGS assays to silence all endogenous TaSARD1 or TaEDS1 genes in the leaf epidermal cell of the B.g. tritici-susceptible wheat cultivar Yannong 999. As shown in Figure 4B, silencing of TaSARD1 or TaEDS1 genes resulted in a notable HI% increase to above 42%, compared to 31% for empty vector controls. In addition, we employed BSMV-VIGS to silence all endogenous TaSARD1 or TaEDS1 genes in the leaves of the B.g. tritici-susceptible wheat cultivar Yannong 999. qRT-PCR showed that   Figure 4A, the B.g. tritici HI% decreased from 54% for the empty vector control to less than 41% on wheat cells overexpressing TaSARD1 or TaEDS1 genes. These results suggested that overexpression of TaSARD1 or TaEDS1 remarkably attenuated wheat post-penetration susceptibility to B.g. tritici.
the endogenous transcript level of TaSARD1 or TaEDS1 was significantly reduced in the indicated VIGS plants ( Figure 4C). Thereafter, these VIGS plants were inoculated with B.g. tritici conidia, and the formation of microcolonies was statistically analyzed. B.g. tritici MI% increased to approximately 65% on BSMV-TaSARD1as plants and 72% on BSMV-TaEDS1as plants, compared with 53% for the BSMV-γ plants ( Figure 4D). These data support that TaSARD1 and TaEDS1 positively regulate the wheat post-penetration resistance to B.g. tritici.  To further examine the function of TaSARD1 and TaEDS1 in regulating wheat-B.g. tritici interaction, we employed the TIGS assays to silence all endogenous TaSARD1 or TaEDS1 genes in the leaf epidermal cell of the B.g. tritici-susceptible wheat cultivar Yannong 999. As shown in Figure 4B, silencing of TaSARD1 or TaEDS1 genes resulted in a notable HI% increase to above 42%, compared to 31% for empty vector controls. In addition, we employed BSMV-VIGS to silence all endogenous TaSARD1 or TaEDS1 genes in the leaves of the B.g. tritici-susceptible wheat cultivar Yannong 999. qRT-PCR showed that the endogenous transcript level of TaSARD1 or TaEDS1 was significantly reduced in the indicated VIGS plants ( Figure 4C). Thereafter, these VIGS plants were inoculated with B.g. tritici conidia, and the formation of microcolonies was statistically analyzed. B.g. tritici MI% increased to approximately 65% on BSMV-TaSARD1as plants and 72% on BSMV-TaEDS1as plants, compared with 53% for the BSMV-γ plants ( Figure 4D). These data support that TaSARD1 and TaEDS1 positively regulate the wheat post-penetration resistance to B.g. tritici.

TaCAMAT2 and TaCAMTA3 Negatively Regulate Expression of TaSARD1 and TaEDS1
To determine the potential regulation of TaCAMAT2 and TaCAMTA3 on the expression of TaSARD1 and TaEDS1 in bread wheat, we employed BSMV-VIGS to silence all endogenous TaCAMAT2 or TaCAMTA3 genes in the leaves of the B.g. tritici-susceptible wheat cultivar Yannong 999. Thereafter, these VIGS plants were inoculated with B.g. tritici conidia, and expression levels of TaSARD1 and TaEDS1 were analyzed. As shown in Figure 5, the silencing of TaCAMAT2 or TaCAMTA3 genes resulted in a marked increase in the expression levels of TaSARD1 and TaEDS1. Significantly, simultaneous silencing of TaCAMAT2 and TaCAMTA3 could lead to a further increase in the expression levels of TaSARD1

TaCAMAT2 and TaCAMTA3 Negatively Regulate Expression of TaSARD1 and TaEDS1
To determine the potential regulation of TaCAMAT2 and TaCAMTA3 on the expression of TaSARD1 and TaEDS1 in bread wheat, we employed BSMV-VIGS to silence all endogenous TaCAMAT2 or TaCAMTA3   Since PR expressions are usually activated in the plant defense responses to biotrophic pathogens like B.g. tritici, we compared the transcript levels of TaPR1, TaPR2, and TaPR5 among BSMV-TaCAMTA2as, BSMV-TaCAMTA3as, BSMV-TaSARD1as, BSMV-TaEDS1as, and BSMV-γ infected plants. As shown in Figure 6A, the expressions of TaPR1, TaPR2, and TaPR5 were remarkably reduced by silencing of TaSARD1 or TaEDS1, further confirming the fact that TaSARD1 and TaEDS1 positively regulate the wheat defense against B.g. tritici. In contrast, the expressions of TaPR1, TaPR2, and TaPR5 were significantly affected by the silencing of TaCAMAT2 or TaCAMTA3 genes ( Figure 6B). Notably, simultaneous silencing of TaCAMAT2 and TaCAMTA3 could lead to a further increase in the activation of TaPR1, TaPR2, and TaPR5 ( Figure 6B), which is consistent with the fact that partially redundant TaCAMTA2 and TaCAMTA3 negatively regulate expressions of the wheat defense genes TaSARD1 and TaEDS1. Since PR expressions are usually activated in the plant defense responses to biotrophic pathogens like B.g. tritici, we compared the transcript levels of TaPR1, TaPR2, and TaPR5 among BSMV-TaCAMTA2as, BSMV-TaCAMTA3as, BSMV-TaSARD1as, BSMV-TaEDS1as, and BSMV-γ infected plants. As shown in Figure 6A, the expressions of TaPR1, TaPR2, and TaPR5 were remarkably reduced by silencing of TaSARD1 or TaEDS1, further confirming the fact that TaSARD1 and TaEDS1 positively regulate the wheat defense against B.g. tritici.
In contrast, the expressions of TaPR1, TaPR2, and TaPR5 were significantly affected by the silencing of TaCAMAT2 or TaCAMTA3 genes ( Figure 6B). Notably, simultaneous silencing of TaCAMAT2 and TaCAMTA3 could lead to a further increase in the activation of TaPR1, TaPR2, and TaPR5 ( Figure 6B), which is consistent with the fact that partially redundant shown as means ± SEs (t-test; ** p < 0.01) from three independent biological replicates.

TaCAMAT2 and TaCAMTA3 Are Wheat S Genes Suppressing Post-Penetration Resistance against B.g. tritici
Powdery mildew, caused by the adapted fungal pathogen B.g. tritici, seriously threatens global wheat production [3,4]. To improve wheat resistance against powdery mildew, it is vital to identify the important genes involved in the regulation of the wheat-B.g. tritici interaction [3,4]. Powdery mildew (Pm) resistance genes and quantitative trait loci (QTL) contributed to wheat resistance to B.g. tritici and have been employed in wheat breeding for powdery mildew resistance [3,4]. Compatibility between wheat and B.g. tritici underlies wheat's susceptibility to powdery mildew. A plethora of wheat S genes have been  Powdery mildew, caused by the adapted fungal pathogen B.g. tritici, seriously threatens global wheat production [3,4]. To improve wheat resistance against powdery mildew, it is vital to identify the important genes involved in the regulation of the wheat-B.g. tritici interaction [3,4]. Powdery mildew (Pm) resistance genes and quantitative trait loci (QTL) contributed to wheat resistance to B.g. tritici and have been employed in wheat breeding for powdery mildew resistance [3,4]. Compatibility between wheat and B.g. tritici underlies wheat's susceptibility to powdery mildew. A plethora of wheat S genes have been identified to facilitate compatibility by inducing B.g. tritici (pre)penetration, suppressing wheat immunity, and supporting the sustenance of B.g. tritici [34,35]. For instance, wheat S genes TaWIN1, TaKCS6, and TaECR were revealed to facilitate the conidial germination of B.g. tritici by promoting the biosynthesis of wheat cuticular wax, whereas wheat S gene TaSTP13 encodes a sugar transporter facilitating wheat hexose accumulation for B.g. tritici acquisition [36][37][38][39][40][41]. TaMLO, TaEDR1, and TaPOD70 genes contribute to wheat susceptibility to powdery mildew by suppressing plant defense responses [42][43][44][45][46][47]. In addition, S factors TaMED25, TaHDA6, TaHOS15, and TaHDT701 positively contribute to wheat susceptibility to B.g. tritici by suppressing defense-related transcriptional reprogramming in bread wheat [48][49][50][51][52][53].
Through homology-based searching, TaCAMAT2 and TaCAMTA3 were identified as the most closely related homologs of AtCAMTA3, which is consistent with the reported phylogenetic analysis of the CAMTA homologs in different species [19]. TaCAMAT2 and TaCAMTA3 are characterized as wheat S genes contributing to the wheat post-penetration susceptibility to B.g. tritici in this study. Overexpression of TaCAMTA2 and TaCAMTA3 in the leaf epidermal cell by transient gene expression assays led to enhanced wheat susceptibility to B.g. tritici, while knockdown of TaCAMTA2 and TaCAMTA3 expression using transient-or virus-induced gene silencing resulted in compromised wheat post-penetration susceptibility to B.g. tritici. Interestingly, a gain-of-function mutation in SIGNAL RESPONSIVE1 (SR1), which encodes the Arabidopsis homologs of wheat TaCAMTA2 and TaCAMTA3, could suppress the edr2-associated powdery mildew resistance [29]. The sr1-4D single mutant is more susceptible to Arabidopsis powdery mildew (Golovinomyces cichoracearum), whereas the sr1-1 null mutant plants displayed enhanced post-penetration resistance against G. cichoracearum [29]. In addition, Arabidopsis AtCAMTA1 was revealed to function partially redundantly with AtCAMTA2 and AtCAMTA3 in suppressing plant immunity [30][31][32]. In this study, simultaneous silencing of TaCAMAT2 and TaCAMTA3 could lead to a further decrease in the HI% and MI% compared with single silencing of TaCAMAT2 or TaCAMTA3, supporting the fact that TaCAMTA3 functions partially redundantly with TaCAMAT2 in suppressing wheat post-penetration resistance against B.g. tritici. In Arabidopsis, CAMTA transcription factors AtCAMTA1, AtCAMTA2, and AtCAMTA3 partially redundantly suppress the biosynthesis of salicylic acid (SA) and N-hydroxypipecolic acid (NHP), a metabolite duo essential for systemic acquired resistance (SAR) [30][31][32]. Therefore, it is intriguing to examine the potential roles of the S genes TaCAMAT2 and TaCAMTA3 in the regulation of SA and NHP biosynthesis, as well as SAR establishment, in bread wheat in future research.

TaSARD1 and TaEDS1 Confer Wheat Post-Penetration Resistance against B.g. tritici
TaSARD1 and TaEDS1 are identified as positive regulators of wheat resistance against B.g. tritici in this study. Overexpression of TaSARD1 or TaEDS1 in the leaf epidermal cell by transient gene expression assays led to enhanced wheat post-penetration resistance to B.g. tritici, while knockdown of TaSARD1 or TaEDS1 expression using transient-or virus-induced gene silencing resulted in increased wheat post-penetration susceptibility to B.g. tritici. In Arabidopsis, transcription factor AtSARD1 functions in concert with AtCBP60g to activate the expression of SID2 (SA INDUCTION DEFICIENT 2), which encodes isochorismate synthase 1 (ICS1), essential for pathogen-induced SA biosynthesis [54][55][56]. Arabidopsis AtEDS1 was shown to heterodimerize with its partners, phytoalexin deficient 4 (PAD4) or senescence-associated gene 101 (SAG101), to play signaling roles in ETI as well as SAdependent and SA-independent PTI pathways [57][58][59][60][61][62][63][64]. Consistent with this, expressions of SA defense marker genes TaPR1, TaPR2, and TaPR5 induced by B.g. tritici infection were attenuated by silencing of TaSARD1 or TaEDS1, suggesting that the SARD1-EDS1-SA defense axis might be partially conserved between model plant Arabidopsis and crop plant bread wheat. Therefore, it is intriguing to examine the potential regulation of wheat SA biosynthesis and signaling by TaSARD1 and TaEDS1 in future research.

TaCAMAT2 and TaCAMTA3
Negatively Regulate the Expression of TaSARD1 and TaEDS1 to Suppress Wheat Post-Penetration Resistance against B.g. tritici In this study, expression levels of TaSARD1 and TaEDS1 were significantly enhanced by silencing TaCAMTA2 and TaCAMTA3. Notably, simultaneous silencing TaCAMAT2 and TaCAMTA3 could lead to a further increase in the expression levels of TaSARD1 and TaEDS1 compared with single silencing TaCAMAT2 or TaCAMTA3, indicating that TaCAMTA2 and TaCAMTA3 partially redundantly suppress expressions of TaSARD1 and TaEDS1. In Arabidopsis, AtCAMTA3 could bind to the promoter region of AtEDS1 by recognizing the CGCG box, thereby directly repressing the expression of AtEDS1 [28][29][30][31]. In addition, the expression of AtSARD1 was demonstrated to be negatively regulated by partially redundant AtCAMTA1, AtCAMTA2, and AtCAMTA3, presumably via an indirect effect [28][29][30][31]. These results indicate that negative regulation of the expressions of defense genes SARD1 and EDS1 by partially redundant CAMTA3 and its homologs might be partly conserved between the model plant Arabidopsis and the important crop bread wheat. Indeed, the expressions of SA defense marker genes TaPR1, TaPR2, and TaPR5 induced by B.g. tritici infection were found to be potentiated by silencing TaCAMAT2 or TaCAMTA3 in this study. However, binding sites for TaCAMAT2 and TaCAMTA3 in the promoter regions of TaSARD1 and TaEDS1 genes remain to be identified.
Herein, TaCAMAT2 and TaCAMTA3 are identified as wheat S genes partially redundantly suppressing post-penetration resistance against powdery mildew, presumably via negative regulation of the expressions of defense genes TaSARD1 and TaEDS1. Genetic manipulation of S genes TaMLO and TaEDR1 via targeting induced local lesions in genomes (TILLING) and genome editing techniques like transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas (CRISPR-associated) 9 systems compromised wheat compatibility with B.g. tritici and conferred wheat resistance against powdery mildew [65][66][67][68][69][70][71][72][73]. Therefore, it is intriguing to examine the potential of manipulating the S genes TaCAMAT2 and TaCAMTA3 in wheat breeding for powdery mildew resistance in future research.

Plant and Fungal Materials
The seedlings of bread wheat cultivar Yannong999 used in this study were grown in a growth chamber under a 16-h/8-h, 20 • C/18 • C day/night cycle with 70% relative humidity. The B.g. tritici strain E09 was maintained on the leaves of Jing411 plants. Conidia of B.g. tritici strain E09 were used for the inoculation of Jing411 leaves in the study of wheat-powdery mildew interaction. Arabidopsis thaliana used in this study was grown in the greenhouse under a 16 h/8 h light period at 23 ± 1 • C with 70% relative humidity.