ORA47 is a transcriptional regulator of a general stress response hub

Abstract

Transcriptional regulators of general stress response (GSR) reprogram expression of selected genes to transduce informational signals into cellular events, ultimately manifested in plants ability to cope with environmental challenges. Identification of the core GSR regulatory proteins will uncover the principal modules and their mode of action in the establishment of adaptive responses. To define the GSR regulatory components, we employed a yeast-one-hybrid assay to identify the protein(s) that binds to the previously established functional GSR motif, coined Rapid Stress Response Element (RSRE). This led to the isolation of ORA47 (octadecanoid-responsive AP2/ERF-domain transcription factor 47), a Methyl jasmonate (MeJA) inducible protein. Subsequently, the ORA47 transcriptional activity was confirmed using RSRE-driven Luciferase (LUC) activity assay performed in the ORA47 loss- and gain-of-function lines introgressed into the 4xRSRE::Luc background. In addition, the prime contribution of CALMODULIN-BINDING TRANSCRIPTIONAL ACTIVATOR3 (CAMTA3) protein in induction of RSRE was reaffirmed by genetic studies. Moreover, exogenous application of MeJA led to enhanced levels of ORA47 and CAMTA3 transcripts, and the induction of RSRE::LUC activity. Metabolic analyses illustrated the reciprocal functional inputs of ORA47 and CAMTA3 in increasing JA levels. Lastly, transient assays identified JASMONATE ZIM-domain1 (JAZ1) as a repressor of RSRE::LUC activity. Collectively, the report provides a fresh insight into the initial mechanistic features of transducing the informational signals into adaptive responses in part via the complex functional interplay between JA biosynthesis/signaling cascade and the transcriptional reprogramming necessary for potentiation of GSR, while offering a window into the role of intraorganellar communication in the establishment of adaptive responses. SignificanceThe work unmasks the initial mechanistic features of adaptive responses that include tight cooperativity between JA biosynthesis and signaling cascade and the nuclear transcriptional machinery comprised of two activators (CAMTA3 and ORA47) and a suppressor JAZ1). The work further identifies CAMTA3 as a functional link between JA signaling and activation of a general stress transcriptional hub.