Abstract
BackgroundBakanae 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.ResultsThis 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.ConclusionsDifferent 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.
Highlights
Bakanae is a seedborne disease caused by Fusarium fujikuroi
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 differentially expressed genes (DEGs) were for the first time shown to be associated with disease resistance, and jasmonic acid (JA)-mediated resistance was identified as a crucial component of rice defense against F. fujikuroi
Summary
Bakanae is a seedborne disease caused by Fusarium fujikuroi. Little is known about rice defense mechanisms at early stages of disease development. Bakanae disease, caused by the heterothallic ascomycete fungus Fusarium fujikuroi Nirenberg, has become a threat to rice quality and yield in recent years. Many studies from Asian countries such as Bangladesh, India, South Korea, Pakistan, and Taiwan have reported the increasing incidence and severity of bakanae disease (Khan et al 2000; Chu et al 2010; Haq et al 2010; Gupta et al 2015; Kim et al 2015). F. fujikuroi is a seed-borne pathogen that can infect rice panicles at the flowering stage (Ou 1985). Because bakanae disease is becoming a serious threat to rice production, it is crucial to develop new control measures from different perspectives
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