Ectopic expression of the persimmon β-galactosidase gene DkGAL2 promotes leaf growth, delays dark-induced senescence and enhances tolerance to abiotic stress in Arabidopsis

Abstract

Plant β-galactosidases (EC 3.2.1.23) have activities related to cell wall galactan-containing polysaccharides metabolism and cell wall remodeling, though their precise functions have not yet been established. We previously isolated a persimmon β-galactosidase gene, DkGAL2, with high levels of transcripts were detected in leaves and during fruit developments. Here, abundant DkGAL2 transcripts were observed in expanding persimmon leaves, increasing with dark-induced senescence but remaining constant with glucose supplementation under dark conditions. The promoter sequence of DkGAL2 harbors several cis-elements related to leaf expansion. To further investigate the role of DkGAL2, ectopic overexpression of DkGAL2 in Arabidopsis was performed, and the leaves of DkGAL2-overexpressing plants exhibited high growth rates and large leaf areas. Moreover, DkGAL2 overexpression enhanced tolerance to abscisic acid (ABA), methyl jasmonate (MeJA) and NaCl, with plants have long root lengths and high galactose contents, suggesting a role for DkGAL2 in abiotic stress responses. In addition, DkGAL2-transgenic plants showed delayed senescence under dark conditions, and some ABA signaling-related genes were significantly suppressed in transgenic plants during senescence compared to WT plants. Together, these results demonstrate that by affecting cell wall modification, DkGAL2 is involved in leaf expansion and senescence. The functions of DkGAL2 might affect ABA signaling during senescence.