FAR-RED ELONGATED HYPOCOTYL3 and FAR-RED IMPAIRED RESPONSE1 Transcription Factors Integrate Light and Abscisic Acid Signaling in Arabidopsis

Abstract

Light and the phytohormone abscisic acid (ABA) regulate overlapping processes in plants, such as seed germination and seedling development. However, the molecular mechanism underlying the interaction between light and ABA signaling is largely unknown. Here, we show that FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and FAR-RED IMPAIRED RESPONSE1 (FAR1), two key positive transcription factors in the phytochrome A pathway, directly bind to the promoter of ABA-Insensitive5 and activate its expression in Arabidopsis (Arabidopsis thaliana). Disruption of FHY3 and/or FAR1 reduces the sensitivity to ABA-mediated inhibition of seed germination, seedling development, and primary root growth. The seed germination of the fhy3 mutant is also less sensitive to salt and osmotic stress than that of the wild type. Constitutive expression of ABA-Insensitive5 restores the seed germination response of fhy3. Furthermore, the expression of several ABA-responsive genes is decreased in the fhy3 and/or far1 mutants during seed imbibition. Consistently, FHY3 and FAR1 transcripts are up-regulated by ABA and abiotic stresses. Moreover, the fhy3 and far1 mutants have wider stomata, lose water faster, and are more sensitive to drought than the wild type. These findings demonstrate that FHY3 and FAR1 are positive regulators of ABA signaling and provide insight into the integration of light and ABA signaling, a process that may allow plants to better adapt to environmental stresses.

Identification of novel genes potentially involved in rice ( Oryza sativa L.) drought tolerance

“…According to Tang and coworkers (2013), FAR1 is a positive regulator of ABA signaling whose expression is induced by various abiotic stresses such as drought, osmosis, and salt. Upregulation of ABA signaling network enables plants to better adapt to environmental stresses (Tang et al, 2013). These examples support the notion that 2 identified transcription factors belonging to this family, namely LOC_Os03g62660.2 and LOC_Os10g34884.1, might play roles in rice drought tolerance.…”

WHIRLY1 Functions in the Control of Responses to Nitrogen Deficiency But Not Aphid Infestation in Barley

“…The FAR1 gene encodes a transposase-related transcription factor that activates the expressions of FAR-RED ELONGATED HYPOCOTYL1 and FHY1-LIKE, which promote the nuclear translocation of phytochrome A, resulting in the activation of phytochrome A-mediated gene expression, such as chloroplast division and chlorophyll biosynthesis (Tang et al, 2012). The FAR1 protein also acts as a positive regulator of ABA signaling in Arabidopsis, enabling adaptation to environmental stresses (Tang et al, 2013). WHIRLY1 has been shown to influence the responsiveness of seedlings to ABA (Isemer et al, 2012a).…”

Putting the brakes on: abscisic acid as a central environmental regulator of stomatal development

“…4). It has recently been demonstrated that FHY3 and FAR1 (FAR-RED ELONGATED HYPOCOTYL 3 and FAR-RED IMPAI-RED RESPONSE 1), transcription factors that transduce phytochrome A-mediated events, are up-regulated by ABA and also bind to and activate the promoter of ABI5 which encodes a transcription factor associated with the regulation of ABA sensitivity, particularly during seed germination (Tang et al, 2013;Fig. 4).…”

“…FHY3 also provides protection for phytochrome A against degradation by COP1 (Saijo et al, 2008). Although stomatal development phenotypes have not been reported, fhy3 and far1 single and double mutants have additively greater stomatal apertures, ABA insensitivity, and transpirational water loss (Tang et al, 2013). FHY3 and to a lesser extent FAR1 are known to have several developmental effects in plants, but understanding their cause is complicated by their effect on the regulation of chloroplast division (Ouyang et al, 2011).…”