The BRANCHING ENZYME1 gene, encoding a glycoside hydrolase family 13 protein, is required for in vitro plant regeneration in Arabidopsis

Abstract

In vitro plant regeneration requires the coordinated action of various enzymes in addition to phytohormones. Here, we report that the Arabidopsis Branching Enzyme 1 (BE1) gene, encoding a putative glycoside hydrolase involved in carbohydrate metabolism, is critical for explant regeneration. A partial loss-of-function mutation of the BE1 gene (be1-3 mutant) severely impaired adventitious shoot formation and somatic embryogenesis but not root formation in tissue culture. An in planta hormone response assay revealed that be1-3 seedlings showed normal response to cytokinin and auxin. The calli formed from be1-3 mutants were less plump than those of wild type hypocotyls. The BE1 gene is mainly expressed in the xylem pericycle of the hypocotyl and root and in dedifferentiated and differentiating calli. Expression levels of BE1 decreases gradually during shoot formation. Consistent with its role in carbohydrate metabolism, mutation of the BE1 gene dramatically reduces the content of glucose and fructose in seeds. Transcriptomic profiles showed 1,860 and 832 differentially expressed genes between the mutant and wild type during callus and shoot development, respectively. Most of them were related to metabolism, hormone signal transduction and stress response. These results indicate that the BE1 gene is involved in organogenesis and somatic embryogenesis by regulating carbohydrate metabolism.