马铃薯晚疫病菌效应子PITG_16427.2的基因序列分析及功能验证

Sequence analysis and functional verification of a Phytophthora infestans effector, PITG16427.2

马铃薯晚疫病的病原是致病疫霉菌(Phytophthora infestans),该病原菌在侵染马铃薯过程中分泌大量RxLR型效应子,但目前绝大多数RxLR效应子的功能和作用机制尚不明确。本研究成功克隆了致病疫霉菌的一个RxLR效应子PITG16427.2,在本氏烟中瞬时表达PITG16427.2,发现该效应子能够抑制6种激发子(INF1、PsojNIP、BAX、SIF2、Avh238、Avh241)激发的植物免疫反应。进一步研究发现,效应子PITG16427.2在晚疫病菌侵染马铃薯早期上调表达。在15个致病疫霉菌株和3个同属菌株中克隆该基因,克隆到氨基酸序列一致性超过93%的同源基因,这些同源基因均能在本氏烟中抑制INF1和Avh241引起的HR,揭示了该效应子在病原卵菌中序列和功能的高度保守性。在本氏烟和马铃薯感病品种Désirée中瞬时表达PITG16427.2,发现该效应子能够显著促进晚疫病菌的侵染。通过qRT-PCR方法检测发现,乙烯信号的相关基因ERF1显著上调,而水杨酸信号相关基因PR1b显著下调,表明PITG16427.2在晚疫病菌侵染过程中可抑制寄主的SA信号途径,促进晚疫病菌侵染。因此,RxLR型效应子PITG16427.2是致病疫霉菌中一个重要的侵染致病因子。

Phytophthora infestans is the pathogenic microbe of late blight, which secrets numerous of RxLR effectors into potato during the infection. However, the function and mechanism of most RxLR effectors remain unclear. In this study, we cloned a RxLR effector of PITG16427.2 from P. infestans. It can suppress the hypersensitive response(HR) caused by six elicitors including INF1, BAX, PsojNIP, SIF2, Avh238 and Avh241 after co-expressing in Nicotiana benthamiana. Furthermore, the expression of PITG16427.2 is up-regulated at the early stage of infection. Homologous sequences of PITG16427.2 were cloned from all 15 isolates of P. infestans and 3 isolates of Phytophthoras which shared over 93% identity at amino acids level. Interestingly, all homologous sequences of PITG16427.2 could suppress the HR caused by expressing INF1 or Avh241 as well as PITG16427.2HLJ, indicating that they are highly conserved in both sequence and function among on the Phytophthoras. Transient expression of PITG16427.2 in Désirée and N. benthamiana promote the colonization of P. infestans. By using qRT-PCR, we identified that the expression of ethylene signaling pathway related gene ERF1 is significantly up-regulated and the salicylic acid signaling pathway related gene PR1 b is down-regulated respectively. The results imply that PITG16427.2 may enhance the plant susceptibility by suppressing the SA signaling pathway. Overall, we concluded that the RxLR effector of PITG16427.2 is an important pathogenic factor for late blight in P. infestans.