Ketoacid Reduction Isomerase (KARI) Play A Role In Cuticle Development In Arabidopsis Thaliana

Branched-chain amino acids(BCAA)are important metabolites in organisms,which are essential for animal growth and development,and are also crucial for nutrient metabolism,growth,development and responses to stresses in plants.The relationship between BCAA metabolism and triacylglycerol(TAG)accumulation has been well studied in humans and lower plants,but the impacts of BCAA homeostasis on lipid metabolism pathway are less known in higher plants.Ketoacid reduction isomerase(KARI)is a key enzyme in BCAA biosynthesis,but its function in plants development is unclear.In order to comprehensively explore the function of KARI in plants,we first checked its expression pattern in Arabidopsis by quantitative PCR and histochemical staining,and found that the transcripts of KARI are abundantly accumulated in regions undergoing cell division and differentiation such as young seedlings,flowers and top stems.In addition,KARI-YFP was identified to reside in chloroplast.In order to study the role of KARI in plant development,we made its antisense construct and transformed it into Arabidopsis thaliana.The transformed plants with low KARI levels show pleiotropic phenotypes such as growth retardation,leaf curling and chlorosis,and plant stunting,indicating that KARI plays an important role in plant growth and development.In addition,we performed a comparative transcriptomic analysis between wild-type and transgenic lines with low KARI levels.Surprisingly,we found that two lipid metabolic pathways were significantly affected in the transgenic lines,i e,genes associated with the cuticle lipid biosynthesis pathway were significantly down-regulated,while genes associated with lipid-derived hormone jasmonic acid(JA)biosynthesis pathway were apparently up-regulated.To further verify the relationship between BCAA metabolism and cuticle development,we also analyzed the components of wax and cutin,and found that profiles of two surface lipids were pronouncedly changed in the transgenic lines.Compared with the wild type,most of cutin monomers and total amount of cutin were notably decreased in the transgenic lines.Although the total amount of wax was little significantly different from that of the wild type,the branched chain wax component was obviously reduced in the transgenic lines.Taken together,these results confirmed that BCAA homeostasis is closely related with cuticle development indeed.In conclusion,our study identified the vital role of KARI in plant growth and development,and also extends our understanding of the relationship between BCAA homeostasis and lipid metabolism.