Action of the AtNF-Y transcription factors in plant stress responses

Plants have evolved complex and highly regulated stress response mechanisms which elicit major transcriptional reprogramming to mitigate stress. Examination and network inference modelling of high resolution temporal transcriptomic datasets across a range of biotic and abiotic stresses, identified the AtNF-Y transcription factor (TF) family as important regulators of stress responses based on their differential expression patterns and high connectivity in gene regulatory networks (GRNs). In plants, each subunit of the heterotrimeric NF-Y complex is encoded by a multigene family; such extensive combinatorial diversity likely evolved to facilitate transcriptional fine-tuning. A comprehensive investigation into the formation of protein-protein interactions amongst all family members, revealed a widespread ability of AtNF-YB and AtNF-YC subunits to heterodimerise, and also identified interactions between AtNF-YA subunits and a subset of AtNF-YCs expressed during stress conditions. Detailed functional analysis of loss- and gain-of-function mutants in five AtNF-Ys identified partially overlapping roles for AtNF-YA2, AtNF-YA4 and AtNF-YA7 in jasmonic acid(JA)-/ abscisic acid (ABA)-mediated signalling, and enabled the generation of local GRNs centred around each AtNF-Y. A promoter fragment from the JA-biosynthetic gene LIPOXYGENASE3, bound five AtNF-YC subunits in yeast one-hybrid assays, implicating AtNF-Y TF complexes in the regulation of this gene and hence, JA biosynthesis. Stable lines of epitope-tagged translational fusions were generated for one of these subunits, AtNF-YC2, and co-immunoprecipitation of the tagged protein complex in vivo successfully identified AtNF-YB2 as an interacting protein. Investigation of the LIPOXYGENASE3 promoter architecture revealed a requirement for two discrete cis-elements for effective AtNF-Y binding, suggesting that cooperative interactions between NF-Y complexes, and conceivably other TFs, are an important mechanism in their transcriptional regulation, with NF-Ys potentially functioning as pioneer TFs.