Cytosolic calcium mediated regulation of miRNAs in rice cultivar N22.

MicroRNAs are critical components of the multi-dimensional regulatory networks in eukaryotic systems. Given their diverse spectrum of function, it is apparent that the transcription, processing as well as activity of the miRNAs themselves is very dynamically regulated. One of the most important and universally implicated signaling molecule is [Ca2+]cyt. It is known to regulate a plethora of developmental and metabolic processes in both plants and animals, however their impact on the regulation of miRNA expression is relatively less explored. The current study employed a combination of internal and external calcium channel inhibitors, to establish that [Ca2+]cyt signatures actively regulate miRNA expression in rice. Involvement of [Ca2+]cyt in regulation of miRNA expression was further confirmed by treatment with calcimycin, the calcium ionophore. Modulation of the cytosolic calcium levels was also found to regulate the drought responsive expression as well as ABA mediated response of miRNA genes in rice seedlings. The study further establishes the role of calmodulins and Calmodulin-binding Transcription Activators (CAMTAs) as important components of the signal transduction schema that regulates miRNA expression. Yeast-one-hybrid assay established that OsCAMTA4 and 6 are involved in the transcriptional regulation of miR156a and miR167h. Thus, the study was able to clearly establish that [Ca2+]cyt is actively involved in regulating expression of miRNA genes both under control and stress conditions.

微小核糖核酸（microRNA, miRNA）是真核生物系统中多维调控网络的关键组成部分。鉴于其功能谱系多样，显而易见，miRNA自身的转录、加工乃至活性均受到严格的动态调控。胞质游离钙离子（[Ca²⁺]cyt）是最为重要且广泛参与的信号分子之一，已知其可调控动植物中大量的发育与代谢过程，但它对miRNA表达调控的影响却尚未得到充分研究。本研究联合使用胞内与胞外钙离子通道抑制剂，证实胞质游离钙离子信号特征可主动调控水稻中的miRNA表达。通过钙离子载体钙霉素（calcimycin）处理，进一步验证了胞质游离钙离子参与miRNA表达调控的结论。研究还发现，调控水稻幼苗的胞质钙离子水平，可影响其miRNA基因的干旱响应表达及脱落酸（abscisic acid, ABA）介导的响应过程。本研究进一步明确了钙调蛋白与钙调蛋白结合转录激活因子（Calmodulin-binding Transcription Activators, CAMTAs）作为调控miRNA表达的信号转导通路重要组分的功能。酵母单杂交实验证实，OsCAMTA4与OsCAMTA6参与了miR156a及miR167h的转录调控。综上，本研究明确证实：在正常及胁迫条件下，胞质游离钙离子均主动参与调控miRNA基因的表达。