Study On The Biological Function Of Receptor-like Kinase JAK1 In Arabidopsis

Jasmonate is an important plant hormone that regulates multiple aspects of plant growth and defense.In resting status,plant endogenous jasmonate content is maintained at a low level;upon external stimuli(e.g.,mechanical wounding,insect feeding,or Botrytis cinerea infection),jasmonate will be rapidly biosynthesized and accumulate to a higher level.The F-box protein COI1 perceives active forms of jasmonate and subsequently binds and ubiquitinizes JAZ proteins for 26S proteasome-mediated degration,which derepresses downstream transcription factors and activates the expression of jasmonates-responsive genes.However,it remains unclear how the synthesis of jasmonate is rapidly initiated upon stresses.In this study,we explored the role of receptor-like kinase JAK1 in wounding-induced jasmonates synthesis and plant defense.JAK1 is a receptor-like kinase with unknown function.Though no transmembrane domain was identified,JAK1 was observed to localize on plant cell membrane when fused with fluorescent protein(GFP)and transiently expressed in tobacco leaves,indicating that JAK might attach to cell membrane by interacting with unknown membrane-associated protein(s).Our gene expression analysis showed JAK1 is an early response gene response to wounding,and the induction of JAK1 by wounding depends on jasmonate receptor COI1.We further found that the expression of JAK1 can be induced by jasmonate in a COI1 and MYC2/MYC3/MYC4-dependent manner,suggesting that jasmonate regulates JAK1 expression through the MYC transcription factors.These results imply that JAK1 may play a role in jasmonate pathway and its activation by wounding.Next,we studied the functions of JAK1 in jasmonate pathway using T-DNA/CRISPR mutants and overexpression transgenic lines.By examining anthocyanin accumulation and root growth inhibition after exogenous jasmomate treatment,we found that neither knocking out nor overexpressing JAK1 affects the sensitivity of plants to jasmonate.Our luciferase complementation assays demonstrated that JAK1 interacts with OPR3,a key enzyme in the biosynthesis of jasmonate,indicating that JAK1 may be involved in the biosynthesis of jasmonate.Consistent with this hypothesis,wounding-induced expression of VSP1,a jasmonate-responsive maker gene,was significantly inhibited in jak1 mutants,and the jak1 mutants were more susceptible to Botrytis cinerea,a necrotrophic plant fungal pathogen whose infection induces jasmonate biosynthesis and activates jasmonate-regulated plant defense.Based on the above-mentioned results,we proposed a model for JAK1 action in jasmonate-mediated plant defense:upon mechanical wounding or insect/pathogen attack,JAK1 interacts with OPR3 and enhances its enzyme activity to rapidly promote the biosynthesis of jasmonate,thereby participating in jasmonate-mediated plant defense responses.However,more experimental data are needed to validate this model and further reveal the detailed mechanisms.