Background

Bakanae is a seedborne disease caused by Fusarium fujikuroi. Rice seedlings emerging from infected seeds can show diverse symptoms such as elongated and slender stem and leaves, pale coloring, a large leaf angle, stunted growth and even death. Little is known about rice defense mechanisms at early stages of disease development.

Results

This study focused on investigating early defenses against F. fujikuroi in a susceptible cultivar, Zerawchanica karatals (ZK), and a resistant cultivar, Tainung 67 (TNG67). Quantitative PCR revealed that F. fujikuroi colonizes the root and stem but not leaf tissues. Illumina sequencing was conducted to analyze the stem transcriptomes of F. fujikuroi-inoculated and mock-inoculated ZK and TNG67 plants collected at 7 days post inoculation (dpi). More differentially expressed genes (DEGs) were identified in ZK (n = 169) than TNG67 (n = 118), and gene ontology terms related to transcription factor activity and phosphorylation were specifically enriched in ZK DEGs. Among the complex phytohormone biosynthesis and signaling pathways, only DEGs involved in the jasmonic acid (JA) signaling pathway were identified. Fourteen DEGs encoding pattern-recognition receptors, transcription factors, and JA signaling pathway components were validated by performing quantitative reverse transcription PCR analysis of individual plants. Significant repression of jasmonate ZIM-domain (JAZ) genes (OsJAZ9, OsJAZ10, and OsJAZ13) at 3 dpi and 7 dpi in both cultivars, indicated the activation of JA signaling during early interactions between rice and F. fujikuroi. Differential expression was not detected for salicylic acid marker genes encoding phenylalanine ammonia-lyase 1 and non-expressor of pathogenesis-related genes 1. Moreover, while MeJA did not affect the viability of F. fujikuroi, MeJA treatment of rice seeds (prior to or after inoculation) alleviated and delayed bakanae disease development in susceptible ZK.

Conclusions

Different from previous transcriptome studies, which analyzed the leaves of infected plants, this study provides insights into defense-related gene expression patterns in F. fujikuroi–colonized rice stem tissues. Twelve out of the 14 selected DEGs were for the first time shown to be associated with disease resistance, and JA-mediated resistance was identified as a crucial component of rice defense against F. fujikuroi. Detailed mechanisms underlying the JA-mediated bakanae resistance and the novel defense-related DEGs are worthy of further investigation.

中文翻译：

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水稻对藤黑镰刀菌早期防御的转录组分析。

背景

Bakanae 是一种由藤黑镰刀菌引起的种传病害。从受感染的种子中长出的水稻幼苗会表现出多种症状，例如茎叶细长、颜色苍白、叶角大、生长发育迟缓甚至死亡。关于疾病发展早期阶段的水稻防御机制知之甚少。

结果

本研究的重点是在易感品种 Zerawchanica karatals (ZK) 和抗性品种 Tainung 67 (TNG67) 中调查对F. fujikuroi 的早期防御。定量 PCR 显示F. fujikuroi定植于根和茎，但不定植于叶组织。进行 Illumina 测序以分析在接种后 7 天 (dpi) 收集的F. fujikuroi接种和模拟接种的 ZK 和 TNG67 植物的茎转录组。在 ZK ( n  = 169)中发现的差异表达基因 (DEG ) 比 TNG67 ( n = 118)，并且与转录因子活性和磷酸化相关的基因本体术语在 ZK DEG 中特别丰富。在复杂的植物激素生物合成和信号通路中，仅鉴定了参与茉莉酸 (JA) 信号通路的 DEG。通过对单个植物进行定量逆转录 PCR 分析，验证了 14 个编码模式识别受体、转录因子和 JA 信号通路组分的 DEG。在 3 dpi 和 7 dpi 两个品种中茉莉酸 ZIM 结构域 ( JAZ ) 基因 ( OsJAZ9、OsJAZ10和OsJAZ13 ) 的显着抑制表明水稻与藤黑镰刀菌早期相互作用期间 JA 信号传导激活. 编码苯丙氨酸解氨酶 1 的水杨酸标记基因和发病相关基因 1 的非表达基因未检测到差异表达。此外，虽然 MeJA 不影响F. fujikuroi的活力，但 MeJA 处理水稻种子（之前或之前）接种后) 减轻和延迟了易感 ZK 中的 bakanae 病的发展。

结论

与之前分析受感染植物叶子的转录组研究不同，本研究提供了对F. fujikuroi定植的水稻茎组织中防御相关基因表达模式的见解。14 个选定的 DEG 中有 12 个首次被证明与抗病性有关，并且 JA 介导的抗性被确定为水稻防御藤黑镰刀菌的关键组成部分。JA 介导的 bakanae 抗性和新型防御相关 DEG 的详细机制值得进一步研究。