| Description: |
Four grape 'CBF' genes had been isolated from both the freezing tolerant wild species 'Vitis riparia' and the freezing susceptible cultivated species 'Vitis vinifera' but the functions and differences amongst these genes were virtually unknown. In this study, it was demonstrated that 'CBF' genes from 'V. riparia ' are functional and target to the nucleus if the predicted NLS sequence is present. Both VrCBF1 and VrCBF4 transiently activated the expression of downstream genes via the CRT elements in their promoters and 'in planta ' they activated the expression of the 'Arabidopsis COR' genes 'AtCOR15a, AtCOR6.6, AtRD29A,' and 'AtCOR47.' VrCBF4 appears to activate CRT-containing genes more efficiently than VrCBF1, perhaps because of its preferential binding to the ACCGACNTNA CRT sequence. Functional differences were observed between VrCBF1 (representing the group of VrCBF1, 2, 3) and VrCBF4. VrCBF1 contributed to cold, freezing, drought and salt stress tolerance in 'Arabidopsis' whereas VrCBF4 contributed only to cold and freezing tolerance. In general, stress tolerant ' Arabidopsis' plants were dwarf in size, flowered late and more leaves were produced prior to flowering. They also produced comparatively small and thicker leaves, with a thick palisade and spongy mesophyll layer of cells, suggesting that the architecture of the leaves might help prevent water loss from the plants, and thus contribute to drought tolerance. 'In silico' analysis revealed the presence of basic and ' CBF'-specific regulatory promoter elements in 'CBF1, 2, 3' and '4' promoters of 'V. riparia' and 'V. vinifera. VrCBF1, 2' and '3' genes have shorter 5' UTR than the 'VrCBF4' gene. Functional analyses showed that 1.6 kb of 'VrCBF1' and ~1 kb of 'VrCBF3 ' and 'VrCBF4' promoters are sufficient to impart cold regulated gene expression and that 'VrCBF1' expresses in the growing region and young leaves whereas 'VrCBF4' expresses mostly in older tissues of transgenic 'Arabidopsis' plants, as expected based on the expression of the endogenous genes ... |