StMPK7 phosphorylates and stabilizes a potato RNA-binding protein StUBA2a/b to enhance plant defence responses

Abstract

Mitogen-activated protein kinase (MAPK) cascades play pivotal roles in regulating plant immunity. MAPKs usually transduce signals and regulate plant immunity by phosphorylating the downstream defence-related components. Our previous study indicates that StMPK7 positively regulates plant defence to Phytophthora pathogens via SA signalling pathway. However, the downstream component of StMPK7 remains unknown. In this study, we employed GFP-StMPK7 transgenic potato and performed immunoprecipitation-mass spectrometry (IP-MS) to identify the downstream component of StMPK7. We found that an RNA binding protein StUBA2a/b interacted with StMPK7, as revealed by luciferase complementation imaging (LCI) and coimmunoprecipitation (co-IP) assays. Transient expression of StUBA2a/b in N. benthamiana enhanced plant resistance to Phytophthora pathogens, while silencing of UBA2a/b decreased the resistance, suggesting a positive regulator role of UBA2a/b in plant immunity. Similar to StMPK7, StUBA2a/b was also involved in SA signalling pathway and induced SGT1-dependent cell death as constitutively activated (CA)-StMPK7 did. Immune blotting indicated that StMPK7 phosphorylates StUBA2a/b at thr248 and thr408 (T248/408) sites and stabilizes StUBA2a/b. Silencing of MPK7 in N. benthamiana suppressed StUBA2a/b-induced cell death, while co-expression with StMPK7 enhanced the cell death. Besides, StUBA2a/bT248/408A mutant showed decreased ability to trigger cell death and elevate the expression of PR genes, indicating the phosphorylation by StMPK7 enhances the functions of StUBA2a/b. Moreover, CA-StMPK7-induced cell death was largely suppressed by silencing of NbUBA2a/b, genetically implying UBA2a/b acts as the downstream component of StMPK7. Collectively, our results reveal that StMPK7 phosphorylates and stabilizes its downstream substrate StUBA2a/b to enhance plant immunity via the SA signalling pathway.

The potato StMKK5‐StSIPK module enhances resistance to Phytophthora pathogens through activating the salicylic acid and ethylene signalling pathways

“…N. benthamiana is an ideal model host plant to study the molecular mechanisms of immunity of solanaceous plants against oomycetes belonging to the Phytophthora genus (Du et al, 2021 ; Li et al, 2022 ; Matsukawa et al, 2013 ; Shibata et al, 2016 ; Zhang et al, 2021 ). In our cDNA‐VIGS screen in N. benthamiana , we tested in total 384 Agrobacterium colonies containing random TRV2 plasmids (unpublished data), and we found that VIGS driven by one Agrobacterium colony containing a TRV2 plasmid with an insert of which the nucleotide sequence matches with a N. benthamiana MAPKK gene ( Niben101Scf01249g04006 ) resulted in an enhanced susceptibility to P. infestans .…”

“…According to the phylogenetic tree of solanaceous MAPKK proteins, we renamed this gene as NbMKK5. To (Du et al, 2021;Li et al, 2022;Matsukawa et al, 2013;Shibata et al, 2016;Zhang et al, 2021).…”

Phytophthora infestans RXLR effector Pi23014 targets host RNA‐binding protein NbRBP3a to suppress plant immunity

“…The expression of TaRZ1 in Arabidopsis also affects many genes related to plant growth and stress response (Xu et al., 2015 ). RBP StUBA2a/b also positively regulates plant defence against Phytophthora pathogens via the salicylic acid (SA) signalling pathway (Li et al., 2022 ).…”