Isolation of an abscisic acid senescence and ripening inducible gene from litchi and functional characterization under water stress.

A full-length abscisic acid (ABA) senescence and ripening inducible gene named LcAsr was obtained from litchi. Bioinformatic analysis showed that full-length LcAsr was 1,177 bp and contained an open reading frame (ORF) encoding 153 amino acids, 85- and 146-bp 5' and 3' UTRs, respectively. LcAsr was expressed in all organs, with preferential expression in the flower and low levels in pulp. The expression level of LcAsr in postharvest uncovered fruit reached a maximum at 24 h after harvest. When the litchi fruit was covered with plastic film, the LcAsr expression level remained constant. LcASR protein localized in the nucleus. LcAsr was transformed in Arabidopsis thaliana L. (ecotype Columbia) and four transgenic lines were obtained. One line, 35S::LcAsrD, was selected for drought tolerance analysis and showed higher tolerance to drought than the control. The activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase were much higher in the transgenic line than the control under drought conditions. The levels of several ABA/stress-regulated genes were investigated. The transcript level of responsive to ABA (RAB18) remained constant and responsive to dehydration (RD29A) displayed a slight decrease in the Columbia line (Col). However, the transcript levels of LcAsr, RAB18, and RD29A were greatly enhanced in the transgenic 35S::LcAsrD. The transcript levels of KAT1, KAT2, and SKOR were also markedly decreased in the transgenic line. These results suggest an important role of LcAsr as a protective molecule for water deficit and help to understand the molecular mechanism of postharvest litchi fruit dehydration.