Promoter activities of genes encoding β-galactosidases from Arabidopsis a1 subfamily.

Promoter regions of each of the six AtBGAL gene of the subfamily a1 of Arabidopsis thaliana were used to drive the expression of the β-glucuronidase gene. The pattern of promoters (pAtBGAL) activity was followed by histological staining during plant development. pAtBGAL1, pAtBGAL3 and pAtBGAL4 showed a similar activity pattern, being stronger in cells and organs in expansion, and the staining decreasing when cell expansion decreased with age. That indicates a consistent involvement of the encoded β-galactosidases in cells undergoing cell wall extension or remodelling in cotyledons, leaves and flower buds. These promoters were also active in the calyptra cells and in pollen grains. pAtBGAL2 activity showed a clear relationship with hypocotyl elongation in both light and dark conditions and, like pAtBGAL1, pAtBGAL3 and pAtBGAL4, it was detected during the expansion of cotyledons, rosette leaves and cauline leaves. Its activity was also intense in the early stages of flower and fruit development. pAtBGAL5 was the only one among those from the subfamily a1 that was active in the trichomes that appear throughout the plant, indicating a high specificity of the AtBGAL5 protein and its involvement in the cell wall changes that accompany the formation of the trichome. The activity of pAtBGAL5 was also high in radicles and roots, except in the meristematic area of these organs, and during seed formation. Finally, the activity of pAtBGAL12 was mainly detected in meristematic zones of the plant: the leaf primordium, emerging secondary roots and developing seeds, which indicates an involvement in the differentiation process.