Research ArticleTaNAC6s are involved in the basal and broad-spectrum resistance to powdery mildew in wheat
Introduction
Plants are often invaded by bacteria, fungi and viruses throughout the whole life cycle, which forces them to evolve a series of sophisticated disease resistance mechanism to cope with multiple biotic stresses. Transcriptional regulation of gene expression is a common event during the growth and development, and it is also a universe mechanism adopted by plants to adapt to unfavorable environments. Transcription factors (TF) play important roles in regulating the expression level of various genes by activating or inhibiting the transcription of the target genes by interacting with a specific DNA sequence in the promoter region [1]. TF families, such as AP2/ERF, bZIP, WRKY, MYB, bHLH and NAC, have been found to be widely involved in disease resistance pathways [2,3].
NAC (NAM, ATAF1,2, and CUC2) TFs are one of the largest families specifically in plants [2]. Based on the whole genome sequencing and bioinformatics analysis, a large number of NAC TFs have been screened from various plant species, for instance, 151 NAC TFs in rice, 117 in Arabidopsis, 148 in maize and 152 in soybeans [[4], [5], [6]], respectively. According to the protein structure analysis, NAC domain is composed of five motifs A–E, and NAC TFs are classified into six types [1]. NAC TFs typically contain a highly conserved N-terminal region which is responsible for binding to the cis-elements in the promoter region of target genes or directly binding to target proteins, whereas the C-terminal region is more diverse which is responsible for transcription activation or repression of target genes [1].
NACs were originally identified as key regulators of development in plants. For example, No Apical Meristem (NAM) in Petunia was the first explored NAC required for formation of apical meristem and primordia boundaries, then different NAM and CUC members with similar function were found in other species, such as CUC1, CUC2 and CUC3 in Arabidopsis [[7], [8], [9], [10]], CUP in Antirrhinum majus [11], ZmNAM1, ZmNAM2 and ZmCUC3 in maize [12], and OsNAC2 in rice [13]. In addition, NACs were also found to be widely involved in seed germination, cell division, secondary wall thickening, lateral root development, flowering, and senescence [[14], [15], [16]]. Recently, more and more evidences supported that NACs are involved in the responses to abiotic and biotic stresses. ANAC019, ANAC055 and OsNAC9 were found to positively regulate the drought tolerance, and overexpression of them could enhance the drought tolerance in Arabidopsis and rice, respectively [17,18]. However, AtNAP plays negative role in drought tolerance, and silencing of it made Arabidopsis more tolerant to drought [19].
Many NACs have been found to be involved in response to biotic stress. Among them, some played positive roles in plant resistance against pathogen. For instance, OsNAC6, OsNAC111, ONAC122 and ONAC131 positively regulate rice resistance against blast disease, and OsNAC58 contributes to rice resistance against bacterial leaf blight disease [[20], [21], [22], [23]]. In Arabidopsis, overexpression of NTL6 enhanced resistance against Pseudomonas syringae pv. tomato DC3000 by inducing the expression of PR genes [24]. However, some NACs perform as negative regulators in plant resistance against pathogen. In Arabidopsis, overexpression of ANAC019 or ANAC055 reduced resistance against Botrytis cinereal [25]. In wheat, TaNAC1, 2 and 30 play negative roles in resistance against stripe rust [[26], [27], [28]]. Some NACs regulate different stresses responses simultaneously perhaps by manipulating a series of genes with similar cis-elements. For example, overexpression of OsNAC6 enhanced rice tolerance to dehydration and high-salt stresses and increased resistance to blast disease [20], and overexpression of SNAC2 increased rice tolerance to cold, salt and drought [29].
Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a widespread epidemic disease in wheat all over the world [30]. Due to the rapid evolution of Bgt isolates, isolate-specific resistance genes usually undergo breakdown after large-scale application in production. So, broad-spectrum resistance genes show a great advantage for its often-accompanied durability. According to the difference of triggers, resistance is classified into two types, one is pathogen associated molecular pattern (PAMP)-triggered immunity as PTI or basal resistance, another is effector-triggered immunity as ETI or specific resistance. Several genes are identified to be involved not only in the broad-spectrum resistance but also in the basal resistance. In our previous study, two materials showing broad-spectrum resistance were developed, one is NAU9918 created by chromosome engineering which carrying the broad-spectrum powdery mildew resistance gene Pm21 from the wild species Haynaldia villosa and showing immunity to all the tested Bgt isolates inside and outside of China, the other is OEStpk-V created by genetic engineering which overexpressing of the Stpk-V gene and showing broad-spectrum to 29 individual Bgt isolates [31]. It is interesting to explore the broad-spectrum resistance related genes in these two lines. HvNAC6 was reported to be involved in the basal resistance to Blumeria graminis f. sp. Hordei (Bgh), and its orthologous gene ATAF1 in Arabidopsis was involved in the nonhost resistance to Bgh [32]. In this study, the roles of three homoeologous members of TaNAC6s in the broad-spectrum resistance to Bgt were functionally analyzed in wheat. It was found that TaNAC6-A, TaNAC6-B and TaNAC6-D have different response patterns but similar resistance functions to Bgt. The rapid response of HvNAC6 to Bgh in barley and the quick response of TaNAC6s to both Bgt and Bgh in wheat implied that the conserved resistance pathway to Blumeria graminis mediated by NAC6 was formed before the divergency of barley and wheat.
Section snippets
Plant materials and fungal isolates
Wheat cv. NAU9918 is a wheat-H. villosa translocation T6VS·6AL with a broad-spectrum resistance gene Pm21 to powdery mildew on 6VS chromosome arm developed by Cytogenetics Institute of Nanjing Agricultural University (CINAU), and its isogenic susceptible line SM-1 is an EMS-induced Bgt-susceptible mutant of NAU9918 [33]. OEStpk-V is a descendant of Stpk-V overexpressed transgenic line with broad-spectrum resistance to Bgt described in Cao et al. [31], and its isogenic susceptible line wheat cv.
Isolation and sequences analysis of TaNAC6s
In our previous studies, two isogenic lines were developed, one is Pm21-containing NAU9918 and its EMS-induced mutant SM-1, another is Stpk-V-overexpressed transgenic OEStpk-V and its recipient Yangmai158. NAU9918 and OEStpk-V showed broad-spectrum resistance to powdery mildew with IT 0 to 0;, while SM-1 and Yangmai158 showed high susceptibility to powdery mildew with IT 4. So, these two groups of isogenic lines are perfect materials to study the broad-spectrum powdery mildew resistance. To
Discussion
In wheat, more than 134 NAC genes were predicted and a few of them have been functionally studied [26]. TaNAC2, 27, 47, 69 were positively involved in abiotic stress revealed by overexpression in Arabidopis or wheat [2,[38], [39], [40]]. TaNAC1, 2, 8, 30 were negatively involved in stripe rust resistance revealed by VIGS analysis [[26], [27], [28],41]. As to TaNAC6s, they were previously found to be induced by salt and drought stress [42], but the role of TaNAC6s in the resistance to biotic
Acknowledgements
This work was supported by the Important National Science and Technology Specific Projects of Transgenic Research (Grant No. 2018ZX0800905B), the Natural Science Foundation of China (Grant No. 31671685, 31771779, 31471489), the Natural Science Foundation of Jiangsu Province (Grant No. SBK2017020263), the Fundamental Research Funds for the National Central Universities (Grant No. KYZ201601, KYYJ201602).
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The role of NAC genes in response to biotic stresses in plants
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2022, Plant Physiology and BiochemistryCitation Excerpt :It was reported that bread wheat TaNAC1, TaNAC21/22 and TaNAC30 negatively regulate the resistance to phytopathogen fungus and their silencing enhanced the resistance against Puccinia striiformis f. sp. tritici in wheat (Feng et al., 2014). Moreover, the overexpression of TaNAC6-A confers resistance to Blumeria graminis, while the silencing all TaNAC6 homeologs resulted in enhanced susceptibility against B. graminis (Zhou et al., 2018). Furthermore, the silencing of two potato NAC genes StNTP1 and StNTP2, which to the NTL subfamily, increased the resistance to pathogenic fungi in potato (McLellan et al., 2013).
Genetic dissection of the powdery mildew resistance in wheat breeding line LS5082 using BSR-Seq
2022, Crop JournalCitation Excerpt :Relatively little is known regarding the molecular mechanism of powdery mildew resistance in wheat. For example, only the R genes Pm1 and Pm4, and the transcription factors NAC (NAM ATAF1/2 CUC2) and MYB (V-myb avian myeloblastosis viral oncogene homolog), have been analyzed in depth [20,24,32,33]. In the identification and dissection of wheat resistance genes, bulked segregant RNA-seq (BSR-seq), which combines RNA sequencing (RNA-seq) and bulked segregant analysis (BSA), provides a highly efficient and low-cost method to rapidly map an R gene and to profile the pattern of differentially expressed genes associated with that R gene [34,35].
TaNAC032 transcription factor regulates lignin-biosynthetic genes to combat Fusarium head blight in wheat
2021, Plant ScienceCitation Excerpt :For instance, the silencing of TaNAC1, TaNAC21/22, or TaNAC30 showed enhanced resistance against Puccinia striformis f. sp. tritici, whereas TaNAC30 negatively regulated stripe rust resistance in wheat [28–30]. Overexpression of TaNAC6 suggested enhanced resistance against Blumeris graminis f. sp. tritici (Bgt), while silencing compromised the resistance, further confirming the role of TaNAC6 in resistance against Bgt [31]. In Arabidopsis thaliana, secondary wall-associated NAC domain protein (SND1) and vascular-related NAC domain 7 (VND7) functions as the master regulators of secondary wall biosynthesis in fibers and vessels [32,33].
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These authors contributed equally to this work.