Subtilisin-like serine protease secreted by pathogenic fungi can facilitate the infection and acquisition of nutrients. Functions of subtilisin-like serine proteases in the phytopathogenic fungus Alternaria alternata remains unknown. In the current study, 15 subtilisin-like serine proteases were individually deleted in the citrus fungal pathogen A. alternata. Only one, designated AaPrb1, was found to be required for A. alternata pathogenesis. The AaPrb1 deficiency strain (ΔAaprb1) reduced growth, conidiation, the formation of aerial hyphae, protease production, and virulence on citrus leaves. However, biochemical analyses and bioassays revealed that ΔAaprb1 plays no role in the production of ACT toxin. Through Y2H assays, Aaprb1 was found to interact with Aapep4, a vacuole-localized proteinase A in A. alternata. Furthermore, silencing AaPep4 in A. alternata resulted in phenotypes similar with those of ΔAaprb1. Expression of AaPrb1 was found to be regulated by AaPep4. TEM showed that AaPrb1and AaPep4 were involved in the suppression of the degradation of autophagosomes. Deletion of the autophagy gene AaAtg8 in A. alternata decreased conidiation, the formation of aerial hyphae and pathogenicity similar to ΔAaprb1, implying that some phenotypes of ΔAaprb1 were due to the impairment of autophagy. Overall, this study expands our understanding of how A. alternata utilizes the subtilisin-like serine protease to achieve successful infection in the plant host.

病原性真菌分泌的枯草杆菌蛋白酶样丝氨酸蛋白酶可以促进营养的感染和获取。枯草杆菌蛋白酶样丝氨酸蛋白酶在植物致病真菌链格孢中的功能仍然未知。在当前的研究中，柑橘类真菌病原体A. alternata中分别缺失了15种枯草杆菌蛋白酶样丝氨酸蛋白酶。只有一个，指定AaPrb1，后来发现需要为A.病菌致病。AaPrb1缺乏菌株（ΔAaprb1）减少了柑橘叶片的生长，分生，气生菌丝的形成，蛋白酶的产生和毒力。然而，生化分析和生物测定表明，ΔAaprb1在ACT毒素的产生中不起作用。通过Y2H检测，Aaprb1被发现与Aapep4，在液泡本地化的蛋白酶一个交互链格孢。此外，沉默AaPep4在格孢导致与那些Δ的相似的表型Aaprb1。发现AaPrb1的表达受AaPep4调节。TEM显示AaPrb1和AaPep4参与自噬体降解的抑制。自噬基因的缺失AaAtg8在格孢分生孢子接合，气生菌丝和致病性类似于Δ的形成减少Aaprb1，这意味着一些Δ的表型Aaprb1是由于自噬的损害。总的来说，这项研究扩大了我们对交链孢霉如何利用枯草杆菌蛋白酶样丝氨酸蛋白酶在植物宿主中成功感染的理解。