Abstract
Gibberella stalk rot caused by Fusarium graminearum is one of the devastating diseases of maize that causes significant yield losses worldwide. The molecular mechanisms regulating defense against this pathogen remain poorly understood. According to recent studies, a major oxylipin hormone produced by 13-lipoxygenases (LOX) namely jasmonic acid (JA) has been associated with maize susceptibility to GSR. However, the specific roles of numerous 9-LOX-derived oxylipins in defense against Gibberella stalk rot (GSR) remain unexplained. In this study, we have shown that disruption of a 9-LOX gene, ZmLOX5, resulted in increased susceptibility to GSR, indicating its role in defense. To understand how ZmLOX5 regulates GSR resistance, we conducted transcriptome and oxylipin profiling using a zmlox5-3 mutant and near-isogenic wild type B73, upon infection with F. graminearum. The results showed that JA biosynthetic pathway genes were highly up-regulated, whereas multiple 9-LOX pathway genes were down-regulated in the infected zmlox5-3 mutant. Furthermore, oxylipin profiling of the mutant revealed significantly higher contents of several jasmonates but relatively lower levels of 9-oxylipins in zmlox5-3 upon infection. In contrast, B73 and W438, a more resistant inbred line, displayed relatively lower levels of JAs, but a considerable increase of 9-oxylipins. These results suggest antagonistic interaction between 9-oxylipins and JAs, wherein 9-oxylipins contribute to resistance while JAs facilitate susceptibility to F. graminearum.
Highlights
Gibberella stalk rot caused by Fusarium graminearum severely impacts maize (Zea mays) production worldwide, leading to dramatic yield losses (Mueller and Wise, 2015)
Jasmonic acid (JA) biosynthesis is initiated by oxidation of α-linolenic acid by 13-LOXs followed by the action of allene oxide synthase (AOS) and allene oxide cyclase (AOC) resulting in the production of a JA precursor, 12-oxo-phytodienoic acid (12-OPDA)
The other 9-LOX genes, ZmLOX4, ZmLOX5, and ZmLOX12 were reported to be required for defense against F. verticillioides in maize, as lox4 and lox5 mutants were susceptible to F. verticillioides, accompanied by decreased levels of JAs (Park, 2012; Christensen et al, 2014; Battilani et al, 2018, Lanubile et al, 2021)
Summary
Gibberella stalk rot caused by Fusarium graminearum (teleomorph Gibberella zeae) severely impacts maize (Zea mays) production worldwide, leading to dramatic yield losses (Mueller and Wise, 2015). Disruption of ZmCCT, a candidate gene for qRfg, reduced Fusarium spp. resistance (Wang et al, 2017), while ZmAuxRp1, a candidate gene for qRfg, exerts its function via balancing the growth and defense by regulating DIMBOA content upon F. graminearum infection (Ye et al, 2019). Despite these findings, the complex mechanisms underlying maize resistance to GSR remain largely unexplored. It is concluded that ZmLOX5produced 9-oxylipins contribute to GSR resistance, whereas JAs appear to facilitate F. graminearum virulence
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