Browsing by Author "Deb, Sohini"

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    Interaction of the Xanthomonas effectors XopQ and XopX results in induction of rice immune responses
    (John Wiley & Sons, 2020) Deb, Sohini; Ghosh, Palash; Patel, Hitendra K.; Sonti, Ramesh V.
    Xanthomonas oryzae pv. oryzae uses several type III secretion system (T3SS) secreted effectors, namely XopN, XopQ, XopX, and XopZ, to suppress rice immune responses that are induced following treatment with cell wall degrading enzymes. Here we show that a T3SS secreted effector XopX interacts with two of the eight rice 14‐3‐3 proteins. Mutants of XopX that are defective in 14‐3‐3 binding are also defective in suppression of immune responses, suggesting that interaction with 14‐3‐3 proteins is required for suppression of host innate immunity. However, Agrobacterium mediated delivery of both XopQ and XopX into rice cells results in induction of rice immune responses. These immune responses are not observed when either protein is individually delivered into rice cells. XopQ‐ XopX induced rice immune responses are not observed with a XopX mutant that is defective in 14‐3‐3 binding. Yeast two‐ hybrid, BiFC and co‐ IP assays indicate that XopQ and XopX interact with each other. A screen for Xanthomonas effectors which can suppress XopQ‐ XopX induced rice immune responses, led to the identification of five effectors, namely XopU, XopV, XopP, XopG and AvrBs2, that could individually suppress these immune responses. These results suggest a complex interplay of Xanthomonas T3SS effectors in suppression of both pathogen triggered immunity and effector triggered immunity to promote virulence on rice.
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    Xanthomonas oryzae pv. oryzae XopQ protein suppresses rice immune responses through interaction with two 14-3-3 proteins but its phospho-null mutant induces rice immune responses and interacts with another 14-3-3 protein
    (John Wiley & Sons, 2019) Deb, Sohini; Gupta, Mahesh K.; Patel, Hitendra K.; Sonti, Ramesh V.
    Many bacterial phytopathogens employ effectors secreted through the type-III secretion system to suppress plant innate immune responses. The Xanthomonas type-III secreted non-TAL effector protein Xanthomonas outer protein Q (XopQ) exhibits homology to nucleoside hydrolases. Previous work indicated that mutations which affect the biochemical activity of XopQ fail to affect its ability to suppress rice innate immune responses, suggesting that the effector might be acting through some other pathway or mechanism. In this study, we show that XopQ interacts in yeast and in planta with two rice 14-3-3 proteins, Gf14f and Gf14g. A serine to alanine mutation (S65A) of a 14-3-3 interaction motif in XopQ abolishes the ability of XopQ to interact with the two 14-3-3 proteins and to suppress innate immunity. Surprisingly, the S65A mutant gains the ability to interact with a third 14-3-3 protein that is a negative regulator of innate immunity. The XopQS65A mutant is an inducer of rice immune responses and this property is dominant over the wild-type function of XopQ. Taken together, these results suggest that XopQ targets the rice 14-3-3 mediated immune response pathway and that its differential phosphorylation might enable interaction with alternative 14-3-3 proteins.