The F-box protein ZmFBL41 negatively regulates disease resistance to Rhizoctonia solani by degrading the abscisic acid synthase ZmNCED6 in maize.

KEY MESSAGE: The maize F-box protein ZmFBL41 targets abscisic acid synthase 9-cis-epoxycarotenoid dioxygenase 6 for degradation, and this regulatory module is exploited by Rhizoctonia solani to promote infection. F-box proteins are crucial regulators of plant growth, development, and responses to abiotic and biotic stresses. Previous research identified the F-box gene ZmFBL41 as a negative regulator of maize (Zea mays) defenses against Rhizoctonia solani. However, the precise mechanisms by which F-box proteins mediate resistance to R. solani remain poorly understood. In this study, we show that ZmFBL41 interacts with an abscisic acid (ABA) synthase, 9-cis-epoxycarotenoid dioxygenase 6 (ZmNCED6), promoting its degradation via the ubiquitination pathway. We discovered that the ectopic overexpression of ZmNCED6 in rice (Oryza sativa) inhibited R. solani infection by activating stomatal closure, callose deposition, and jasmonic acid (JA) biosynthesis, indicating that ZmNCED6 enhances plant immunity against R. solani. Natural variation at ZmFBL41 across different maize haplotypes did not affect the ZmFBL41-ZmNCED6 interaction. These findings suggest that ZmFBL41 targets ZmNCED6 for degradation, leading to a decrease in ABA levels in maize, in turn, inhibiting ABA-mediated disease resistance pathways, such as stomatal closure, callose deposition, and JA biosynthesis, ultimately facilitating R. solani infection.

Transcriptome analysis reveals genes potentially related to maize resistance to Rhizoctonia solani.

Banded leaf and sheath blight (BLSB) is a devasting disease caused by the necrotrophic fungus Rhizoctonia solani that affects maize (Zea mays L.) fields worldwide, especially in China and Southeast Asia. Understanding how maize plants respond to R. solani infection is a key step towards controlling the spread of this fungal pathogen. In this study, we determined the transcriptome of maize plants infected by a low-virulence strain (LVS) and a high-virulence strain (HVS) of R. solani for 3 and 5 days by transcriptome deep-sequencing (RNA-seq). We identified 3,015 (for LVS infection) and 1,628 (for HVS infection) differentially expressed genes (DEGs). We confirmed the expression profiles of 10 randomly selected DEGs by quantitative reverse transcription PCR. We also performed a Gene Ontology (GO) enrichment analysis to establish which biological processes are associated with these DEGs, which revealed the enrichment of defense-related GO terms in LVS- and HVS-regulated genes. We selected 388 DEGs upregulated upon fungal infection as possible candidate genes. Among them, the overexpression of ZmNAC41 (encoding NAC transcription factor 41) or ZmBAK1 (encoding BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1) in rice enhanced resistance to R. solani. In addition, overexpressing ZmBAK1 in rice also increased plant height, plant weight, thousand-grain weight, and grain length. The identification of 388 potential key maize genes related to resistance to R. solani provides significant insights into improving BLSB resistance.