Decreased accumulation of glutelin types in rice grains constitutively expressing a sunflower seed albumin gene

Differential accumulation of three classes of glutelin proteins and a globulin in sunflower seed albumin (SSA) transgenic rice seeds were observed with 2-DE. Sulfur nutrition did not affect the accumulation of SSA but the levels of four identified glutelins and the globulin were lower in transgenic seeds compared to non-transgenic seeds. Such re-allocation of sulfur reserves from endogenous proteins to the sulfur sink in transgenic grain is suggestive of a transcriptional control of sulfur mobilization in plants. Previous studies have shown differential accumulation of sulfur rich glutelins and sulfur poor prolamins in transgenic rice seeds expressing a sunflower seed albumin gene [Hagan, N.D., Upadhyaya, N., Tabe, L.M., Higgins, T.J., 2003. The redistribution of protein sulfur in transgenic rice expressing a gene for a foreign, sulfur-rich protein. Plant J 34, 1–11]. Here, we show, by two-dimensional electrophoresis, differential accumulation of three classes of glutelin proteins – type I, II and III – and a globulin, not previously resolved, in transgenic seeds grown under low and high sulfur nutrition. Several glutelin polypeptides were resolved and four identified as a type I glutelin, two type II glutelins and a type III glutelin. Although sulfur nutrition did not affect the accumulation of sunflower seed albumin, the levels of all four identified glutelins and the globulin were lower in mature seeds derived from transgenic plants grown under sulfur-optimum or sulfur limited conditions compared to non-transgenic rice seeds. The reduction of all four glutelin polypeptides and the globulin varied from 21% to 68%. The re-allocation of sulfur reserves from endogenous proteins to the sulfur sink in transgenic grain is suggestive of a transcriptional control of sulfur mobilization in plants.