Characterization of a tissue-specific and developmentally regulated beta-1,3-glucanase gene in pea (Pisum sativum)

As part of a search for seed coat-specific expressed genes in Pisum sativum cv. Finale by PCR-based methods, we identified and isolated a cDNA encoding a beta- 1,3-glucanase, designated PsGNS2. The deduced peptide sequence of PsGNS2 is similar to a subfamily of beta-1,3-glucanases, which is characterized by the presence of a long amino acid extension at the C-terminal end compared to the other beta-1,3-glucanases. PsGNS2 is expressed in young flowers and in the seed coat and is weakly expressed in vegetative tissues (roots and stems) during seedling development. It is not inducible by environmental stress or in response to fungal infection. In developing pea flowers the transcript is detectable in all four whirls. In the seed coat the expression is temporally and spatially regulated. High abundance of the transcript became visible in the seed coat when the embryo reached the late heart stage and remained until the mid seed-filling stage. In situ hybridization data demonstrated that the expression of PsGNS2 is restricted to a strip of the inner parenchyma tissue of the seed coat, which is involved in temporary starch accumulation and embryo nutrition. This tissue showed also less callose deposits than the other ones. The 5' genomic region of PsGNS2 was isolated and promoter activity studies in transgenic Medicago truncatula showed a seed-specific expression. Highest activity of the promoter was found in the seed coat and in the endosperm part of the seed.