Calcium‐dependent protein kinase CPK28 targets the methionine adenosyltransferases for degradation by the 26S proteasome and affects ethylene biosynthesis and lignin deposition in Arabidopsis. (24th March 2017)

• Record Type: Journal Article
• Authors: Jin, Yu; Ye, Nenghui; Zhu, Fuyuan; Li, Haoxuan; Wang, Juan; Jiang, Liwen; Zhang, Jianhua
• Is Part Of: Plant journal. Volume 90:Number 2(2017)
• Page Start: 304
• Page End: 318
• Publication Date: 2017-03-24
• Subjects: calcium‐dependent protein kinase 28 -- ethylene -- lignification -- methionine adenosyltransferase -- post‐translational modification -- 26S proteasome; Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.13493
• Languages: English
• ISSNs: 0960-7412

Abstract

Summary: S ‐adenosylmethionine (AdoMet) is synthesized by methionine adenosyltransferase (MAT), and plays an essential role in ethylene biosynthesis and other methylation reactions. Despite increasing knowledge of MAT regulation at transcriptional levels, how MAT is post‐translationally regulated remains unknown in plant cells. Phosphorylation is an important post‐translational modification for regulating the activity of enzymes, protein function and signaling transduction. Using molecular and biochemical approaches, we have identified the phosphorylation of MAT proteins by calcium‐dependent protein kinase (CPK28). Phenotypically, both MAT2‐overexpressing transgenic plants and cpk28 mutants display short hypocotyls and ectopic lignifications. Their shortened hypocotyl phenotypes are caused by ethylene overproduction and rescued by ethylene biosynthesis inhibitor aminoethoxyvinylglycine treatment. Genetic evidence reveals that MAT2 mutation restores the phenotype of ectopic lignification in CPK28‐deficient plants. We find that total MAT proteins and AdoMet are increased in cpk28 mutants, but decreased in CPK28‐overexpressing seedlings. We also find that MATs in OE::CPK28 are degraded through the 26S proteasome pathway. Our work suggests that CPK28 targets MATs (MAT1, MAT2 and MAT3) for degradation by the 26S proteasome pathway, and thus affects ethylene biosynthesis and lignin deposition in Arabidopsis. Significance Statement: S‐adenosylmethionine (AdoMet) is synthesized by methionine adenosyltransferases (MATs) and plays an essential role in ethylene biosynthesis and other methylation reactions. Although transcriptional control of MATs has been well studied, how MATs are post‐translationally regulated in plants is unclear. Here we show that phosphorylation of MATs targets them for degradation through the ubiqutin/26s proteasome pathway.