Molecular cloning and expression analysis of seven sucrose synthase genes in bamboo (Bambusa emeiensis): investigation of possible roles in the regulation of cellulose biosynthesis and response to hormones

Sucrose synthase (SUS, EC 2.4.1.13) is a key enzyme involved in sucrose metabolism. In this study, amplification by polymerase chain reaction confirmed that there are at least seven SUS genes (BeSUS1-7) in the Bambusa emeiensis genome. The expression patterns of the BeSUSs genes differed from each other in various bamboo tissues. Among these BeSUSs, BeSUS2 was expressed predominately in the root and BeSUS5 was most abundant in developing shoots, indicating that these two isozymes might play more important physiological roles in root and shoot than the other BeSUSs genes, respectively. In addition, BeSUSs response to abscisic acid (ABA), methyl jasmonate (MeJA) and 2,6-dichlorobenzonitrile treatment (2,6-DCB, an inhibitor of cellulose synthesis) was also investigated in leaves. The results showed that the expression levels of the BeSUS1, 5 and 7 genes were not only conspicuously induced by ABA treatment but also up-regulated by exogenous application of MeJA, indicating that these three isozymes are most likely involved in ABA and MeJA stress responses and are important in meeting the increased glycolytic demand that occurs during these stresses. Moreover, after 2,6-DCB treatment, the cellulose content of leaves was decreased and the transcripts of BeSUS2, 3 and 7 were markedly decreased, while those of BeSUS 5 and 6 were conspicuously induced. The results suggest that the possible roles of BeSUSs genes in the pathway of sucrose metabolism, bamboo resistance to abiotic stresses and the regulation of cellulose biosynthesis may be divergent.