Sequence polymorphism, gene transcriptional pattern and function analysis of the RXLR effector PcAvh2 from Phytophthora capsici

Abstract:

[Objective] The aim was to analyze the sequence polymorphism, gene transcriptional pattern and functions of the RXLR effector PcAvh2 from Phytophthora capsici.[Methods] We cloned PcAvh2 gene by high-fidelity PCR from 31 P. capsici isolates, 2 P. parasitica isolates and 1 P. cactorum isolate. Gene expression changes during the developmental stages (mycelia, zoosporangia, zoospores and germinated cysts) and infection period (1.5, 3, 6, 12, 24, 36, 72 h post-inoculation) of P. capsici were monitored by quantitative RT-PCR. PVX-based agroinfiltration assay was performed to examine if PcAvh2 could suppress plant immunity triggered by 6 effectors (BAX, INF1, PsojNIP, PsCRN63, PsAvh241 and R3a/Avr3a). The CaCl₂/PEG-mediated protoplast transformation of P. capsici was conducted to silence PcAvh2 and determine if its silencing affected the pathogen's virulence.[Results] PcAvh2 is a typical RXLR effector and possesses 10 alleles in the population. Furthermore, it also exists in P. parasitica and P. cactorum. The expression of PcAvh2 was up-regulated during the host infection by P. capsici. It can suppress the plant immunity induced by all 6 effectors. Intriguingly, silencing of PcAvh2 in P. capsici significantly compromised the pathogen's virulence on host plants.[Conclusion] RXLR effector PcAvh2 is one of important pathogenicity factors in P. capsici.

Key words:Phytophthora capsici;RXLR effector;sequence polymorphism;RT-PCR;plant immunity;gene silencing