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Title: Distinct function of COAR and B3 domains of maize VP1 in induction of ectopic gene expression and plant developmental phenotypes in Arabidopsis

item SUZUKI, MASAHARU - University Of Florida
item WU, SHAN - University Of Florida
item Li, Qin-Bao
item MCCARTY, DONALD - University Of Florida

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2014
Publication Date: 3/1/2014
Citation: Suzuki, M., Wu, S., Li, Q., Mccarty, D.R. 2014. Distinct function of COAR and B3 domains of maize VP1 in induction of ectopic gene expression and plant developmental phenotypes in Arabidopsis. Plant Molecular Biology. 85:179-191.

Interpretive Summary: Arabidopsis ABI3 and maize VP1 are orthologous transcription factors that regulate seed maturation.ABI3 and VP1 have a C-terminal B3 DNA binding domain and a conserved N-terminal co-activator/co-repressor (COAR) domain consisting of A1, B1, B2 sub-domains. The COAR domain mediates abscisic acid signaling via aphysical interaction with ABI5-related bZIP proteins. In order to delineate the COAR and B3 domain dependent functions of VP1, we created site directed mutations in theB3 domain that disrupted DNA binding activity and characterized gene regulation by the mutant proteins in transgenicabi3 mutant Arabidopsis plants. In seeds, COAR domain function of VP1 mutants that lacked B3 DNA binding activity was sufficient for complementation of the desiccation intolerant seed phenotype of abi3. Similarly in seedlings, the B3 domain was dispensable for most VP1 induced gene expression and ectopic developmental phenotypes, except for a small subset of the genes that showed B3 dependent regulation.

Technical Abstract: Maize VP1 enhancement of ABA sensitivity in roots is B3 independent. ABA and VP1 mediated suppression of auxin induced lateral root development is B3 independent. Arabidopsis transgenic system to delineate B3 dependent and COAR domain dependent regulatory functions of VP1. Analyses of ectopic ABA response phenotypes conferred by two DNA binding deficient B3 domain mutations indicate that the B3 domain is required for a discrete subset of ABA regulated gene expression; whereas, the N-terminal COAR domain is sufficient for enhanced ABA sensitivity of root elongation and VP1 mediated interactions of ABA and altered auxin signaling in roots. Intriguingly, a sterility phenotype conferred by ectopic expression of the VP1-K519R mutation suggests developmentally specific functions of the B3 domain that do not require DNA binding activity. The sterility phenotype is caused by physical incompatibility between an elongated pistil and shortened stamens. The resulting flower morphology resembles the longistyly flower type that occurs naturally in plants such as Primula that have a heterostyly mechanism of self-incompatibility.