The VIVIPAROUS (VP1) or ZmABI1 gene from Zea mays is encoded by the gene model Zm00001eb143690 (B73 V5) and was the founding member of this transcription factor family. The ortholog of Vp1 in Arabidopsis thaliana is the ABSCISIC ACID-INSENSITIVE3 (ABI3) gene (AT3G24650). Maize embryos normally become dormant in the seed stage and remain so until conditions favorable for growth are provided. In plants with mutations of this gene mutant kernels germinate before the ear matures (viviparous) and the developing embryos are insensitive to exogenous abscisic acid. It was found that expression of C1, a MYB regulatory gene for the anthocyanin pathway, is selectively blocked at the mRNA level in vp1 mutant seed tissues, indicating the Vp1 may control the anthocyanin pathway by regulating C1 (McCarty et al., 1989). The cloned gene was found to encode a novel DNA transcription factor with an acidic DNA binding domain (McCarty et al., 1991). The VP1 harbors this C-terminal B3 DNA binding domain between amino acids 518-613 (pFAM motif PF02362)(Suzuki et al., 1997). Some related proteins also have a second AP2 DNA binding domain PF00847. Later it was found that the sequence from positions -142 to -132 (cgtcCATGCA(TG)) of the C1 gene is essential for VP1 activation (Kao et al., 1996). This motif is known as the Sph/RY motif in Arabidopsis and is found in the promoter of many seed specific promoters. ZmVP1 may have both activator and repressor functions (Hoecker et al., 1995).Analysis of a maize ABA deficient vp1 vp5 (phytoene desaturase) double mutant indicates that ABA synthesized in the embryo interacts additively with Vp1 to prevent precocious induction of alpha-amylase genes in the aleurone of the developing seed (Hoecker et al., 1999).
In Arabidopsis, ABI3 (AT3G24650) is a central regulator in ABA signaling and is unstable in vivo. It interacts with and can be polyubiquitinated by AIP2 (AT5G20910) in vivo. Based on double mutant analyses, ABI3 interacts genetically with both FUS3 (AT3G26790 - also a VPI-like protein) and LEC1 (AT1G21970 - a CCAAT-HAP3 family member) and is involved in controlling accumulation of chlorophyll and anthocyanins, sensitivity to abscisic acid, and expression of the members of the 12S storage protein gene family. In addition, both FUS3 and LEC1 regulate positively the abundance of the ABI3 protein in the seed. Alternative splicing of ABI3 is developmentally regulated by SUA (AT3G54230). The role of related B3 domain transcription factors in maize kernel filling has also been described (Grimault et al., 2015).
Last updated June 2023 by John Gray
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