Identification and Functional Analysis of S-AdenosylMethionine Synthetase (HvSAMS) genes in Early Maturing Barley (Hordeum vulgare subsp. vulgare)

Grain development has been shown to involve a complex series of physiological and molecular events. In order to provide information on molecular events during grain development, we isolated four noble genes, HvSAMS1, 2, 3 and 4 (Hordeum vulgare S-AdenosylMethionine Synthetase1, 2, 3 and 4). The four HvSAMS genes were closely related based on peptide comparisons and sequence homologies that ranged from 89% to 99%. To determine the developmental expression of HvSAMS genes, Northern blot analysis and RT-PCR were performed with the kernels of -3 to 30 days after fertilization (DAF). The transcripts of HvSAMS1 and 3 genes peaked at -3 DAF that lasted until 7 DAF, and started to reduce at 10 DAF. A strong expression signal of HvSAMS2 was detected from -3 DAF and reached the maximum level at 3 DAF, then decreased until 30 DAF. The expression of HvSAMS4 initially elevated from -3 DAF, reaching the peak at 10 DAF, and decreased gradually until 30 DAF. The HvSAMS gene transcripts were accumulated abundantly in grains, stems and leaves. To evaluate subcellular localization molecular functions of HvSAMS1 gene, we transformed the HvSAMS1 gene into onion epidermal cell and Arabidopsis. Expression of HvSAMS1 recognized by 35S::HvSAMS1::GFP was detected in the nucleus and slightly in the cytosol, whereas 35S::GFP expressed throughout the cell. The transgenic lines showed slightly early germination on MS-medium containing 1 μM GA3 coupled with accelerated extension of bolts. The HvSAMS genes were dominantly expressed in grains during grain development (3 DAF). The HvSAMS genes showed various transcript accumulations in response to the abiotic stresses and exogenous application of phytohormones. Especially, HvSAMS genes were regulated by exogenous GA3. The subcellular localization of HvSAMS1 and histochemical localization of HvSAMS2 promoter provided opportunities to elucidate their possible cellular functions. The phenotypic attributes displayed by HvSAMS1 overexpressing transgenic plants suggested the role of HvSAMS1 in the germination and GA3 response mechanism.