PROTEIN PHOSPHATASE 2A-B′γ Controls Botrytis cinerea Resistance and Developmental Leaf Senescence

Abstract

Plants optimize their growth and survival through highly integrated regulatory networks that coordinate defensive measures and developmental transitions in response to environmental cues. Protein phosphatase 2A (PP2A) is a key signaling component that controls stress reactions and growth at different stages of plant development, and the PP2A regulatory subunit PP2A-B9g is required for negative regulation of pathogenesis responses and for maintenance of cell homeostasis in short-day conditions. Here, we report molecular mechanisms by which PP2A-B9g regulates Botrytis cinerea resistance and leaf senescence in Arabidopsis (Arabidopsis thaliana). We extend the molecular functionality of PP2A-B9g to a protein kinase-phosphatase interaction with the defense-associated calcium-dependent protein kinase CPK1 and present indications this interaction may function to control CPK1 activity. In presenescent leaf tissues, PP2A-B9g is also required to negatively control the expression of salicylic acid-related defense genes, which have recently proven vital in plant resistance to necrotrophic fungal pathogens. In addition, we find the premature leaf yellowing of pp2a-b9g depends on salicylic acid biosynthesis via SALICYLIC ACID INDUCTION DEFICIENT2 and bears the hallmarks of developmental leaf senescence. We propose PP2A-B9g agedependently controls salicylic acid-related signaling in plant immunity and developmental leaf senescence.

Calcium-Dependent Protein Kinase CPK1 Controls Cell Death by In Vivo Phosphorylation of Senescence Master Regulator ORE1

“…These bands most likely represent differentially phosphorylated forms of CPK1, consistent with the literature, where 10 in vivo phosphosites of CPK1 have been listed (PhosPhAt 4.0 database; Durek et al, 2010), or where multiple differentially phosphorylated bands became evident in SDS-gels for the CPK1 ortholog NtCDPK2 from Nicotiana tabacum (Witte et al, 2010). For the native CPK1 protein in wild-type Col-0 plants, which also appears as multiple bands in SDS-gels, it has been shown that slower migrating bands in the PhosTag™ gel system are indeed phosphorylated (Durian et al, 2020). In vitro protein kinase assays with purified, immobilized proteins, originating from leaf material after ethanol incubation, displayed a calcium-dependent increase in phosphorylating activity toward peptide substrate Syntide-2.…”

Age-Dependent Abiotic Stress Resilience in Plants

“…wrky75 mutants not only have reduced SA levels and reduced resistance to P. syringae, but also display delayed senescence. The role of WRKY75 in SA-mediated defense and senescence is antagonistic to PROTEIN PHOSPHATASE 2A-B′γ (PP2A-B′γ), because pp2a-b′γ mutants have higher SA levels, are more resistant to Botrytis cinerea infection, and senesce earlier [132]. These mechanisms illustrate how ARR is achieved through changes in hormone-mediated responses and utilization of chemical defense mechanisms.…”

Genetic Network between Leaf Senescence and Plant Immunity: Crucial Regulatory Nodes and New Insights

“…Contrary to the mpk6 mutants, the MKP2-suppressed line (MPK2_RNAi) displays early senescence phenotypes [35,83]. Another protein phosphatase, phosphatase 2A subunit PP2A-B γ, was recently reported to negatively regulate leaf senescence and resistance against necrotroph B. cinerea, suggesting that MKP2 and PP2A regulate disease resistance against necrotrophs in different mechanisms [98].…”