Phosphoproteins in the primed defense response of plants

植物可以为更快速和强大的防御激活做好准备，这通常伴随着诱导免疫。在拟南芥中，防御启动需要热休克转录辅激活因子HsfB1、防御基因启动子上的组蛋白修饰以及丝裂原激活蛋白激酶MPK3和MPK6的积累（在mRNA转录和蛋白质水平上）。然而，MPK3/6在引物细胞中保持失活状态，需要病原体激活。在病原体攻击时，被引物激活的MPK3/6酶比未被引物激活的多。启动植物中更多mpk的激活与防御基因表达增强和免疫诱导相关。因此，MPK3/6是拟南芥启动的重要调控因子。然而，其他对启动很重要的磷酸化蛋白仍然难以捉摸。我们开发了一种强大的串联金属氧化物亲和层析方法，用于通过LC/MS提取、鉴定和定量低丰度的、可能在启动中起作用的瞬时磷酸化蛋白。在本提案中，我们的目标是表征和功能分析选定的新的候选磷酸化蛋白（例如PEARLI4和TFIIS），它们对拟南芥的防御启动很重要。

Plants can be primed for more rapid and robust activation of defense which often comes with induced immunity. In Arabidopsis thaliana defense priming requires heat shock transcription coactivator HsfB1, histone modifications on defense gene promoters, and accumulation of mitogen-activated protein kinases MPK3 and MPK6 (at both the mRNA transcript and protein levels). However, MPK3/6 are maintained in an inactive state in primed cells and require pathogen challenge for activation. Upon pathogen challenge more MPK3/6 enzymes are activated in primed than in nonprimed cells. The activation of more MPKs in primed plants correlates with enhanced defense gene expression and induction of immunity. Thus, MPK3/6 are important regulators of priming in Arabidopsis. However, other phosphoproteins important for priming remained elusive. We developed a powerful, tandem metal oxide affinity chromatography approach for the extraction, identification, and quantification by LC/MS of low abundant, transiently phosphorylated proteins with a likely role in priming. In the present proposal we aim to characterize, and functionally analyze selected novel phosphoprotein candidates (e.g. PEARLI4 and TFIIS) that are important for defense priming in Arabidopsis.