title: Roles of CAMTA transcription factors and salicylic acid in configuring the low-temperature transcriptome and freezing tolerance of Arabidopsis.
abstract: Previous studies in Arabidopsis thaliana established roles for CALMODULIN BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) in the rapid cold induction of CRT/DRE BINDING FACTOR (CBF) genes CBF1 and CBF2, and the repression of salicylic acid (SA) biosynthesis at warm temperature. Here we show that CAMTA1 and CAMTA2 work in concert with CAMTA3 at low temperature (4°C) to induce peak transcript levels of CBF1, CBF2 and CBF3 at 2 h, contribute to up-regulation of approximately 15% of the genes induced at 24 h, most of which fall outside the CBF pathway, and increase plant freezing tolerance. In addition, CAMTA1, CAMTA2 and CAMTA3 function together to inhibit SA biosynthesis at warm temperature (22°C). However, SA levels increase in Arabidopsis plants that are exposed to low temperature for more than 1 week. We show that this chilling-induced SA biosynthesis proceeds through the isochorismate synthase (ICS) pathway, with cold induction of ICS1 (which encodes ICS), and two genes encoding transcription factors that positively regulate ICS1 - CBP60g and SARD1 -, paralleling SA accumulation. The three CAMTA proteins effectively repress the accumulation of ICS1, CBP60g and SARD1 transcripts at warm temperature but not at low temperature. This impairment of CAMTA function may involve post-transcriptional regulation, as CAMTA transcript levels did not decrease at low temperature. Salicylic acid biosynthesis at low temperature did not contribute to freezing tolerance, but had a major role in configuring the transcriptome, including the induction of 'defense response' genes, suggesting the possible existence of a pre-emptive defense strategy programmed by prolonged chilling temperatures.
authors.affiliation: MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: YongSig
authors.initials: Y
authors.lastname: Kim
authors.forename: Sunchung
authors.initials: S
authors.lastname: Park
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Gilmour
authors.forename: Michael F
authors.initials: MF
authors.lastname: Thomashow
mesh_terms: D000222:Adaptation, Physiological; D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism; D003080:Cold Temperature; D005615:Freezing; D018506:Gene Expression Regulation, Plant; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D020156:Salicylic Acid / Q000378:metabolism*; D013696:Temperature; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D059467:Transcriptome
chemical_list: C572689:AT2G22300 protein, Arabidopsis; D029681:Arabidopsis Proteins; C583820:CAMTA1 protein, Arabidopsis; C104387:CBF1 protein, Arabidopsis; C118228:CBF2 protein, Arabidopsis; D002135:Calcium-Binding Proteins; D002148:Calmodulin-Binding Proteins; C114578:DREB1A protein, Arabidopsis; D015534:Trans-Activators; D014157:Transcription Factors; D019751:Intramolecular Transferases; C058486:isochorismate synthase; D020156:Salicylic Acid
keywords: Arabidopsis thaliana; CAMTA proteins; CBF proteins; freezing tolerance; gene regulation; low temperature; salicylic acid