Exploring membrane-associated NAC transcription factors in Arabidopsis:: implications for membrane biology in genome regulation

Controlled proteolytic cleavage of membrane-associated transcription factors (MTFs) is an intriguing activation strategy that ensures rapid transcriptional responses to incoming stimuli. Several MTFs are known to regulate diverse cellular functions in prokaryotes, yeast, and animals. In Arabidopsis, a few NAC MTFs mediate either cytokinin signaling during cell division or endoplasmic reticulum (ER) stress responses. Through genome-wide analysis, it was found that at least 13 members of the NAC family in Arabidopsis contain strong alpha-helical transmembrane motifs (TMs) in their C-terminal regions and are predicted to be membrane-associated. Interestingly, most of the putative NAC MTF genes are up-regulated by stress conditions, suggesting that they may be involved in stress responses. Notably, transgenic studies revealed that membrane release is essential for the function of NAC MTFs. Transgenic plants overexpressing partial-size NAC constructs devoid of the TMs, but not those overexpressing full-size constructs, showed distinct phenotypic changes, including dwarfed growth and delayed flowering. The rice genome also contains more than six NAC MTFs. Furthermore, the presence of numerous MTFs is predicted in the whole transcription factors in plants. We thus propose that proteolytic activation of MTFs is a genome-wide mechanism regulating plant genomes.