Short communicationExpression patterns of defense genes in resistance of the panicles exserted from the caulis and from the tillers to neck blast in rice
Highlights
► Resistance of rice panicles from different positions to neck blast is different. ► Defense genes in resistance of the panicles from caulis and tillers are different. ► Levels of defense genes in untreated necks from caulis and tillers are different.
Introduction
Rice blast, caused by Magnaporthe oryzae, is the most devastating fungal disease of rice [1]. It has two forms, leaf blast and neck (or panicle) blast, the latter is the major cause of yield losses. The research on rice resistance to neck blast has been receiving increasing attention in recent years, although the difference in resistance shown by the panicles between from the caulis and from various effective tillers (first-class tillers, second-class tillers, etc.) remains one of the neglected aspects [2], [3], [4], [5]. Our work indicates that resistance to neck blast in the panicles from the caulis is positively correlated with that shown by the panicles from tillers in some rice varieties, but in a few varieties these two kinds of panicles differ significantly in the degree of resistance [6].
Plants defend themselves against pathogen challenges by the activation of defense response pathways [7]. The recognition between plant resistance gene products and pathogen avirulence gene products leads to the rapid, coordinated expression of defense genes, whose products participate in fighting back against pathogen infection [8]. The known defense genes in rice mainly encode pathogenesis-related (PR) proteins such as PR1a [9], β-glucanase (Gns) [10], chitinase (Cht) [11], PR4 [12], PR5 [13], and PR10a [14], secondary metabolites such as phenylalanine ammonia-lyase (PAL) [15], chalcone synthase (CHS) [16], and lipoxygenase (LOX) [17], and oxidative stress-related proteins such as peroxidase (POX) [18], and polyphenol oxidase (PPO) [19]. The rapid induction of defense gene expression is required for fighting back against pathogens in plants. The activation speeds and expression levels of defense genes vary in different plant–pathogen interactions.
Our unpublished work indicates that neck blast became progressively severe in the order of emergence of the panicles from the caulis and from 8 effective tillers (5 first-class tillers and 3 second-class tillers) in a rice variety Xiushui227. However, neck blast became gradually alleviative in the order of appearance of the caulis and 9 effective tillers (6 first-class tillers and 3 second-class tillers) in the other variety Xiushui09. The mechanisms controlling defense genes in rice varieties with the difference of resistance to neck blast in the panicles between from the caulis and from tillers are not well understood. In this study, we used these two varieties to examine the induced expression of some known defense genes in the panicles from the caulis and from the first first-class tiller after inoculation with M. oryzae, respectively.
Section snippets
Response of Xiushui227 and Xiushui09 to neck blast
The disease incidence in the necks, disease incidence in the rachis node, lesion length in the necks, and number of conidia in the necks of the panicles exserted from the caulis and from the first first-class tiller in Xiushui227 and Xiushui09 were measured at 10 days post-inoculation with M. oryzae, respectively (data not shown) (Fig. 1). In Xiushui227, no lesions was observed on the inoculated necks of the panicles from the caulis (NPC), whereas there were some typical blast lesions on the
Discussion
Neck blast is a major factor in rice yield loss, and in recent years researchers have paid some attention to neck blast resistance in rice [2], [3], [4], [5]. According to previous reports and our unpublished work, there exist a few rice varieties that resistance to neck blast in the panicles from the caulis differ significantly from that shown by the panicles from various effective tillers [6], thus we should study rice resistance to neck blast in the panicles from the caulis and from tillers,
Plant material and growing conditions
The rice variety Xiushui227 (Oryza sativa L. subsp. japonica) is resistant to neck blast in the panicles from the caulis but susceptible in the panicles from the tillers. However, the other variety Xiushui09 (O. sativa L. subsp. japonica) is susceptible to neck blast in the panicles from the caulis but resistant in the panicles from the tillers. Rice plants were grown under natural light in a greenhouse (20–30 °C) for inoculation experiments. The tillers produced by the caulis were designated
Acknowledgments
This study was funded by Cooperation Project of Zhejiang Academy of Agricultural Sciences and Institute of Genetics and Developmental Biology, Chinese Academy of Sciences; Zhejiang Province Foundation for Natural Science (No. LY12C13005); Advancement Project of Innovation Ability for Science and Technology of Zhejiang Academy of Agricultural Sciences.
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