Many virus genomes encode proteases that facilitate infection. The molecular mechanism of plant recognition of viral proteases is largely unexplored. Using the system of Vigna unguiculata and cowpea mosaic virus (CPMV), we identified a cowpea lipid transfer protein (LTP1) which interacts with CPMV-encoded 24KPro, a cysteine protease, but not with the enzymatically inactive mutant 24KPro(C166A). Biochemical assays showed that LTP1 inhibited 24KPro proteolytic cleavage of the coat protein precursor large coat protein-small coat protein. Transient overexpression of LTP1 in cowpea reduced CPMV infection, whereas RNA interference-mediated LTP1 silencing increased CPMV accumulation in cowpea. LTP1 is mainly localized in the apoplast of uninfected plant cells, and after CPMV infection, most of the LTP1 is relocated to intracellular compartments, including chloroplast. Moreover, in stable LTP1 -transgenic Nicotiana benthamiana plants, LTP1 repressed soybean mosaic virus (SMV) nuclear inclusion a protease activity, and accumulation of SMV was significantly reduced. We propose that cowpea LTP1 suppresses CPMV and SMV accumulation by directly inhibiting viral cysteine protease activity.

中文翻译：

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豇豆脂质转移蛋白1通过抑制豇豆花叶病毒半胱氨酸蛋白酶调节植物防御


许多病毒基因组编码促进感染的蛋白酶。植物识别病毒蛋白酶的分子机制很大程度上尚未被探索。利用豇豆和豇豆花叶病毒（CPMV）系统，我们鉴定了一种豇豆脂质转移蛋白（LTP1），它与CPMV编码的24KPro（一种半胱氨酸蛋白酶）相互作用，但不与酶失活突变体24KPro（C166A）相互作用。生化测定表明，LTP1 抑制外壳蛋白前体大外壳蛋白-小外壳蛋白的 24KPro 蛋白水解切割。豇豆中 LTP1 的瞬时过度表达减少了 CPMV 感染，而 RNA 干扰介导的 LTP1 沉默增加了豇豆中 CPMV 的积累。 LTP1主要定位于未感染植物细胞的质外体中，CPMV感染后，大部分LTP1重新定位到细胞内区室，包括叶绿体。此外，在稳定的LTP1-转基因本塞姆氏烟草植物中，LTP1抑制大豆花叶病毒(SMV)核包涵体蛋白酶活性，并且SMV的积累显着减少。我们提出豇豆 LTP1 通过直接抑制病毒半胱氨酸蛋白酶活性来抑制 CPMV 和 SMV 积累。