Wounding is a general stress in plants that results from various pest and pathogenic infections in addition to environment induced mechanical damages. Plants have sophisticated molecular mechanisms to recognize and respond to pests and pathogens. Although several molecules such as phytohormones, peptides and receptors have been attributed to wound responses in dicots, such mechanisms for monocots probably having distinct wound responses are less understood. Here, we show the involvement of two distinct categories of temporally separated, endogenously derived peptides, namely, plant elicitor peptides (PEPs) and phytosulfokine (PSK), that mediate wound responses in rice. These peptides trigger a dynamic signal relay in which a novel receptor kinase named OsPSKR played a major role. OsPSKR perceived PSK ligand, acting in association with a co-receptor OsSERK1, to activate downstream responses in a kinase activity-dependent manner. Perturbation of OsPSKR expression in rice led to compromised development and constitutive autoimmune phenotypes. These results suggested that OsPSKR maintains the trade-off between growth and exaggerated defense responses, both during homeostasis and wounding. Collectively, these findings indicate the presence of a stepwise peptide-mediated signal relay that regulates the transition from defense to growth upon wounding in monocots.One line summaryEndogenous peptide signalling initiated wound responses through a receptor-like kinase OsPSKR to maintain the balance between growth and defense responses.
Chloroplast is the site for transforming light energy to chemical energy. It also acts as a production unit for a variety of defense-related molecules. These defense moieties are necessary to mount a successful counter defence against pathogens including viruses. Geminiviruses disrupt chloroplast homeostasis as a basic strategy for their successful infection inducing vein-clearing, mosaics and chlorosis in infected plants. Here we show that a geminiviral pathogenicity determinant protein βC1 directly interferes with plastid homeostasis. βC1 was capable of inducing organelle-specific nuclease to degrade plastid genome as well as diverted functions of RecA1 protein, a major player in plastid genome maintenance. βC1 interacted with RecA1 in plants and its homolog in bacteria to reduce the ability of host cells to maintain genomic integrity under stresses. Further, reduction in the coding capacity of plastids severely affected retrograde signalling necessary for viral perception and activation of defense. Induction of chloroplast-specific nuclease by βC1 is similar to phosphate starvation-response in which nucleotides are recycled to augment synthesis of new, potentially viral, DNA. These results indicate the presence of a novel strategy in which a viral protein alters host defence by targeting regulators of chloroplast DNA. We predict that the mechanism identified here might have similarities in other plant-pathogen interactions.
Chloroplast is the site for transforming light energy to chemical energy. It also acts as a production unit for a variety of defense-related molecules. These defense moieties are necessary to mount a successful counter defense against pathogens, including viruses. Previous studies indicated disruption of chloroplast homeostasis as a basic strategy of Begomovirus for its successful infection leading to the production of veinclearing, mosaic, and chlorotic symptoms in infected plants. Although begomoviral pathogenicity determinant protein Beta C1 (bC1) was implicated for pathogenicity, the underlying mechanism was unclear. Here we show that, begomoviral bC1 directly interferes with the host plastid homeostasis. bC1 induced DPD1, an organelle-specific nuclease, implicated in nutrient salvage and senescence, as well as modulated the function of a major plastid genome maintainer protein RecA1, to subvert plastid genome. We show that bC1 was able to physically interact with bacterial RecA and its plant homolog RecA1, resulting in its altered activity. We observed that knocking-down DPD1 during virus infection significantly reduced virus-induced necrosis. These results indicate the presence of a strategy in which a viral protein alters host defense by targeting modulators of chloroplast DNA. We predict that the mechanism identified here might have similarities in other plant-pathogen interactions.
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