MoHRD3基因参与调控稻瘟病菌的生长发育和致病力

 稻瘟病菌(Magnaporthe oryzae)作为主要的农业病原微生物,其引起的稻瘟病严重威胁着水稻等谷类作物的生产安全。内质网相关蛋白质降解途径(Endoplasmic reticulum-associated protein degradation, ERAD)是生物体应答内质网压力的主要方式之一,其在机体生长发育过程中具有重要作用。而HRD(HMG-CoA reductase degradation)复合物作为ERAD的关键组分,主要由Hrd1、Hrd3、以及凝集素Yos9等蛋白组成,负责内质网中错误折叠蛋白的识别、转运以及泛素化过程,最终由蛋白酶体降解,从而有效缓解内质网压力,保证细胞的正常生理活动。有研究表明,Hrd3属于单次跨膜蛋白,在内质网腔中与Hrd1、Yos9相结合,负责底物的识别并起着稳定Hrd1的作用。目前Hrd3在稻瘟病菌中的生物学功能尚不清楚。本研究通过基因敲除及互补试验获得了稻瘟病菌的ΔMohrd3突变体和ΔMohrd3-C回补菌株,并以野生型为对照,对突变体的生物学表型进行了分析。结果显示,ΔMohrd3突变体的生长速率、产孢量明显下降;对大麦和水稻的致病力显著减弱。进一步胁迫试验表明,MoHRD3的缺失导致稻瘟病菌对外界盐胁迫、渗透压胁迫的耐受性增强,对内质网胁迫耐受性减弱,而对细胞壁胁迫无明显变化。同时,MoHRD3基因的缺失激活了未折叠蛋白响应途径(Unfolded protein response, UPR)。上述结果表明,MoHRD3参与调控稻瘟病菌的营养生长、无性繁殖、致病及对不同环境胁迫的响应过程。

MoHRD3 is important in the regulation of the fungal development and pathogenesis of Magnaporthe oryzae

Magnaporthe oryzae is a devastating fungal pathogen that attacks rice and other cereals thus seriously threatening their safe production globally. Endoplasmic reticulum-associated protein degradation (ERAD) is one of the main pathways for the organisms to respond to endoplasmic reticulum (ER) stress. The ERAD pathway also plays an important role in the process of organismal growth and development. The HRD (HMG-COA reductase degradation) complex as a crucial component of ERAD is mainly composed of Hrd1, Hrd3, lectin Yos9, and other proteins. It is responsible for the recognition, transportation, and ubiquitination of misfolded proteins in the ER before their degradation in the proteasome. These cellular processes effectively modulate ER functions and promote the normal physiological metabolism of cells. Previous studies have shown that Hrd3 belongs to a single transmembrane protein, which is bound to Hrd1 and Yos9 in the ER cavity, and is responsible for substrate recognition and plays a role in stabilizing Hrd1. However, the biological function of HRD3 in M. oryzae is still unknown. In this study, we identified and characterized HRD3 in the rice blast fungus. Deletion of MoHRD3 caused defects in vegetative growth and sporulation. Furthermore, the DMohrd3 mutant exhibited a significant reduction in virulence toward both rice and barley. Moreover, deletion of MoHRD3 increased the tolerance of M. oryzae to external salt stress and osmotic stress, but it was more sensitive to ER stress and showed no significant changes to cell wall stress. Loss of MoHRD3 also led to activation of the unfolded protein response (UPR). Taken together, our results show that MoHRD3 is involved in the regulation of vegetative growth, asexual reproduction, pathogenesis and tolerance to different stress conditions.