Abstract
ABI3 (for ABSCISIC ACID INSENSITIVE3), a transcription factor of the abscisic acid signal transduction pathway, plays a major role during seed development, dormancy inception, and dormancy maintenance. This protein appears to also function in meristematic and vegetative plant tissues and under certain stress conditions. We have isolated the ABI3 gene ortholog (CnABI3) from yellow cedar (Callitropsis nootkatensis) and found that it was functionally similar to other ABI3 genes of angiosperms. Here, we report that using a yeast (Saccharomyces cerevisiae) two-hybrid approach, we have identified another protein of yellow cedar (CnAIP2; for CnABI3 INTERACTING PROTEIN2) that physically interacts with CnABI3. Functional analyses revealed that CnAIP2 plays important roles during key transitions in the plant life cycle: (1) CnAIP2 impaired seed development and reduced seed dormancy; (2) CnAIP2 promoted root development, particularly the initiation of lateral roots, and the CnAIP2 gene promoter was exquisitely auxin sensitive; and (3) CnAIP2 promoted the transition from vegetative growth to reproductive initiation (i.e. flowering). The nature of the effects of CnAIP2 on these processes and other evidence place CnAIP2 in the category of a "global" regulator, whose actions are antagonistic to those of ABI3.
Highlights
ABI3, a transcription factor of the abscisic acid signal transduction pathway, plays a major role during seed development, dormancy inception, and dormancy maintenance
Regulation of the expression of an Arabidopsis (Arabidopsis thaliana) 2S storage protein gene (At2S3) appears to involve FUSCA3 (FUS3) and LEAFY COTYLEDON2 (LEC2), both of which bind directly to promoter elements consisting of alternating pyrimidines and purines (RY repeats 1 and 2), and ABI3, which acts in an indirect manner, probably via its interaction with bZIP proteins that bind to the G-box (Kroj et al, 2003)
The complementary DNA fragment of CnAIP2 derived from the pMyr plasmid lacked the 59 end of the coding sequence
Summary
ABI3 (for ABSCISIC ACID INSENSITIVE3), a transcription factor of the abscisic acid signal transduction pathway, plays a major role during seed development, dormancy inception, and dormancy maintenance. This protein appears to function in meristematic and vegetative plant tissues and under certain stress conditions. The broad range of functions of ABI3/VP1 proteins is further exemplified by the fact that they can act as activators or repressors of target genes In this capacity, they do not work alone but in combination with other proteins such as DNAbinding proteins and transcription factors. In rice (Oryza sativa), GF14, a 14-3-3 protein, appears to act as a structural linkage by interacting with both VP1 and EmBP1 as part of the VP1 regulatory complex on the Em gene promoter (Schultz et al, 1998)
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