ABSTRACT

Plant pathogen effector proteins are key to pathogen virulence. In susceptible host Brassicas, the clubroot pathogen, Plasmodiophora brassicae, induces the production of nutrient-sink root galls, at the site of infection. Among a list of 32 P. brassiae effector candidates previously reported by our group, we identified SSPbP53 as a putative apoplastic cystatin-like protein highly expressed during the secondary infection. Here we found that SSPbP53 encoding gene is conserved among several P. brassicae pathotypes and that SSPbP53 is an apoplastic protein able to directly interact with and inhibit cruciferous papain-like cysteine proteases (PLCPs), specifically Arabidopsis XYLEM CYSTEINE PEPTIDASE 1 (AtXCP1). The severity of clubroot disease is greatly reduced in the Arabidopsis xcp1 null mutant (AtΔxcp1) after infection with P. brassicae resting spores, indicating that the interaction of P. brassicae SSPbP53 with XCP1 is important to clubroot susceptibility. SSPbP53 is the first cystatin-like effector identified and characterized for a plant pathogenic protist.

摘要

植物病原体效应蛋白是病原体毒力的关键。在易感宿主芸薹属中，根肿病病原体，芸苔疟原虫，在感染部位诱导产生营养汇根瘿。在我们小组先前报道的 32 个P. brasiae效应候选者的列表中，我们将 SSPbP53 鉴定为在继发感染期间高度表达的推定的质外半胱氨酸蛋白酶抑制剂样蛋白。在这里，我们发现 SSPbP53 编码基因在几种P. brasicae 致病型中是保守的，并且 SSPbP53 是一种质外体蛋白，能够直接与十字花科木瓜蛋白酶样半胱氨酸蛋白酶 (PLCPs) 相互作用并抑制它们，特别是拟南芥 XYLEM CYSTEINE PEPTIDASE 1 ( AtXCP1)。拟南芥xcp1无效突变体 ( At Δ xcp1 ) 在感染P. brasicae 静息孢子后，根肿病的严重程度大大降低，表明P. brasicae SSPbP53 与 XCP1 的相互作用对根肿易感性很重要。SSPbP53 是第一个为植物致病性原生生物鉴定和表征的胱抑素样效应物。