Various environmental stresses limit plant growth, development, and reproductive success. Plants have therefore evolved sophisticated adaptive responses to deal with environmental challenges. The responses of plants to environmental stresses are mainly mediated by abscisic acid (ABA)-dependent and ABA-independent signaling pathways. While these two pathways have been implicated to play discrete roles in abiotic stress responses, accumulating evidence suggests that they are also intertwined. Here, we report that an R2R3-type MYB transcription factor, MYB96, integrates the ABA and cold signaling pathways. In addition to its role in ABA-mediated drought responses, MYB96 is also induced by cold stress in an ABA-independent manner and subsequently activates freezing tolerance. Notably, MYB96 regulates HEPTAHELICAL PROTEIN (HHP) genes by binding to their promoters. The HHP proteins, in turn, interact with C-REPEAT BINDING FACTOR (CBF) upstream regulators, such as INDUCER OF CBF EXPRESSION 1 (ICE1), ICE2, and CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3). The specific interactive networks of HHPs with the CBF upstream regulators are necessary to facilitate transcriptional activation of the CBF regulon under stressful conditions. Together, the MYB96-HHP module integrates ABA-dependent and ABA-independent signals and activates the CBF pathway, ensuring plant adaptation to a wide range of adverse environmental fluctuations.
Keywords: ABA; CBF; HHP; MYB96; cold response.
© 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.