MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
MSU Plant Resilience Institute, Michigan State University, East Lansing, MI, 48824, USA.
Plant J. 2022 Oct;112(1):235-248. doi: 10.1111/tpj.15944. Epub 2022 Sep 9.
The calmodulin-binding transcription activator (CAMTA) proteins of Arabidopsis thaliana play a major role in cold acclimation, contributing to the rapid induction of the C-REPEAT BINDING FACTOR (CBF) genes and other genes that impart freezing tolerance in plants exposed to cold temperature (4°C). The goal of this study was to better understand how the gene induction activity of CAMTA3 is modulated by temperature. Our results indicate that a severely truncated version of CAMTA3, CAMTA3 , which includes the N-terminal CG-1 DNA binding domain and a newly identified transcriptional activation domain (TAD), was able to rapidly induce the expression of CBF2 and two newly identified target genes, EXPANSIN-LIKE A1 (EXPL1) and NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3), in response to cold temperature. Additionally, CAMTA3 was able to restore freezing tolerance when expressed in a camta23 double mutant. The ability of CAMTA3 and CAMTA3 to induce target genes at cold temperature did not involve increased levels of these proteins or increased binding of these proteins to target gene promoters in cold-treated plants. Rather, domain-swapping experiments indicated that the CAMTA3 CG-1 domain conferred temperature dependence to the ability of the CAMTA3 TAD to induce gene expression. The CG-1 domain also enabled the TAD to induce the expression of target genes at a moderate temperature (22°C) in response to cycloheximide treatment, consistent with the TAD activity not being intrinsically temperature dependent. We propose a working model in which the temperature modulation of CAMTA3 gene induction activity occurs independently from the C-terminal calmodulin-binding domains that previously have been proposed to activate CAMTA3 transcriptional activity in response to cold temperature.
拟南芥的钙调素结合转录激活因子（CAMTA）蛋白在冷驯化中起着重要作用，有助于快速诱导 C-重复结合因子（CBF）基因和其他基因的表达，这些基因赋予植物在低温（4°C）下的抗冻性。本研究的目的是更好地了解 CAMTA3 的基因诱导活性如何受温度调节。我们的结果表明，CAMTA3 的一个严重截断版本 CAMTA3 ，它包含 N 端 CG-1 DNA 结合结构域和新鉴定的转录激活结构域（TAD），能够快速诱导 CBF2 和两个新鉴定的靶基因 EXPANSIN-LIKE A1（EXPL1）和 NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3（NCED3）的表达，以响应低温。此外，CAMTA3 能够在 camta23 双突变体中表达时恢复抗冻性。CAMTA3 和 CAMTA3 在低温下诱导靶基因的能力不涉及这些蛋白质水平的增加，也不涉及这些蛋白质在冷处理植物中与靶基因启动子的结合增加。相反，结构域交换实验表明，CAMTA3 的 CG-1 结构域赋予 CAMTA3 TAD 诱导基因表达的能力对温度的依赖性。CG-1 结构域还使 TAD 能够在中等温度（22°C）下响应环己酰亚胺处理诱导靶基因的表达，这与 TAD 活性不具有内在温度依赖性一致。我们提出了一个工作模型，其中 CAMTA3 基因诱导活性的温度调节独立于先前提出的与冷温度反应中激活 CAMTA3 转录活性的 C 端钙调素结合结构域。
