Summary
E3 ubiquitin ligases, as key components of the protein ubiquitination process, play a crucial role in rice immunity. We previously demonstrated that the E3 ligase OsBBI1 modulates rice blast resistance.
Here, we report the OsBBI1-OsSUI1-nonsense-mediated mRNA decay (NMD)-alternatively splicing (AS) network as a regulatory mechanism of OsBBI1 in rice immunity.
OsBBI1 ubiquitinates the eukaryotic translation initiation factor OsSUI1 for degradation. Knockout mutant ossui1 exhibited enhanced resistance to blast and bacterial blight diseases and displayed over-accumulation of defense-related AS transcripts, which was also elevated in OsBBI1-OE plants, including OsDR11S that positively modulates blast resistance. The impaired chitin-triggered immune responses in osbbi1 mutants were partially rescued by OsSUI1 mutation. The NMD factors, for example OsUPF1, OsUPF3, and OsSMG7, were upregulated in ossui1 and OsBBI1-OE plants. Knockdown mutants osupf1, osupf3, and ossmg7 over-accumulated defense-related AS transcripts and enhanced disease resistance. The chitin-triggered immune responses in ossui1 depended on alterations in downstream genes, including the NMD genes and defense-related AS transcripts. OsBBI1 regulated OsSUI1 and OsSMG7 accumulation, while OsSUI1 influenced OsSMG7. Blast fungus infection and chitin treatment decreased OsSUI1 and OsSMG7 levels.
These findings suggest that OsBBI1-mediated degradation of OsSUI1 modulates the NMD pathway, leading to the accumulation of defense-related AS transcripts and enhanced rice immunity.
概括
E3泛素连接酶作为蛋白质泛素化过程的关键组分，在水稻免疫中起着至关重要的作用。前期研究发现，RING类型E3连接酶OsBBI1通过修饰细胞壁防卫反应调控水稻对稻瘟病的抗性。
本研究进一步揭示了OsBBI1-OsSUI1-无义介导的mRNA衰变(NMD)-选择性剪接(AS)网络调控水稻免疫反应的新机制。
OsBBI1泛素化并促进真核翻译起始因子OsSUI1的降解，敲除突变体ossui1对稻瘟病和白叶枯病的抗性增强，稻瘟病菌诱导的活性氧增加，细胞壁增厚，分子式样触发的免疫增强。此外，ossui1和OsBBI1-OE植株中与防御相关的AS转录物过度积累，包括正调控抗病性的OsDR11S。OsSUI1突变后部分恢复了osbbi1突变体中几丁质引发的免疫反应。NMD因子OsUPF1、OsUPF2、OsUPF3和OsSMG7在ossui1和OsBBI1-OE植株中表达上调。敲低突变体osupf1、osupf3和ossmg7中防御相关AS转录物过度积累，免疫力增强。几丁质引发的ossui1免疫应答的升高依赖于下游基因OsUPF1、OsSMG7、OsDR11L和OsDR11S的改变。OsBBI1调节OsSUI1和OsSMG7的积累，而OsSUI1影响OsSMG7的水平。稻瘟病菌和几丁质处理降低了OsSUI1和OsSMG7的蛋白水平。
以上结果表明，OsBBI1介导的OsSUI1降解调节了NMD途径，导致免疫相关AS转录物的积累，增强了水稻的免疫力。本研究揭示了OsBBI1靶向的OsSUI1通过NMD途径负调控水稻免疫的分子机制。
