Trivalent ions activate abscisic acid-inducible promoters through an ABI1-dependent pathway in rice protoplasts

The plant hormone abscisic acid (ABA) mediates many vital processes in plan t growth and development, including seed dormancy, cell division, water use efficiency, and adaptation to drought, salinity, chilling, pathogen attack , and UV light. Our understanding of ABA signal transduction is fragmentary and would benefit from specific and facile probes of the process. Protopla sts from rice (Oryza sativa L. cv IR54) embryonic suspension cultures cotra nsformed with effector plasmids encoding the maize (Zea mays) VIVIPAROUS1 c DNA and/or the Arabidopsis dominant negative mutant (abi1-1) ABA-insensitiv e cDNA demonstrated genetic interactions of VIVIPAROUS1 and abi1-1 in trans activation of the ABA-inducible HVA1 promoter from barley (Hordeum vulgare) , suggesting the mechanisms of these effecters are conserved among monocots and dicots. Trivalent ions have been shown to act as an effector of gene e xpression in plants and animals, although the mechanism of action is unknow n. We show in two complementary transient ABA-inducible gene expression ass ays (beta-glucuronidase and luciferase enzymatic activities and quantitativ e flow cytometry of green fluorescent protein) that trivalent ions specific ally interact with an ABI1-dependent ABA-signaling pathway leading to gene expression. Trivalent ions mimic ABA effects on gene expression and may be a useful tool to study ABA signaling.