Iida H, Furuichi T, Nakano M, Toyota M, Sokabe M, Tatsumi H
Department of Biology, Tokyo Gakugei University, Tokyo, Japan.
Plant Biol (Stuttg). 2014 Jan;16 Suppl 1:39-42. doi: 10.1111/plb.12044. Epub 2013 Jun 4.
The mechano-sensitive channels of plants may sense increases in tension induced by mechanical stimuli, such as touch, wind and turgor pressure, and a gravitational stimulus. Recent studies have identified plant homologues of the bacterial mechano-sensitive channel MscS, which is gated by membrane tension and reduces intracellular osmolality by releasing small osmolytes from bacterial cells. However, the physiological roles of these homologues have not yet been clearly elucidated, and only two of them have been shown to be involved in the protection of osmotically stressed plastids in Arabidopsis thaliana. We identified another group of candidates for mechano-sensitive channels in Arabidopsis, named MCA1 and MCA2, whose homologues are exclusively found in plant genomes. MCA1 and MCA2 are composed of 421 and 416 amino acid residues, respectively, share 73% homology in their amino acid sequences, and are not homologous to any known ion channels or transporters. Our structural study revealed that the N-terminal region (one to 173 amino acids) of both proteins was necessary and sufficient for Ca(2+) influx activity. Interestingly, this region had one putative transmembrane segment containing an Asp residue whose substitution mutation abolished this activity. Our physiological study suggested that MCA1 expressed at the root tip was required for sensing the hardness of the agar medium or soil. In addition, MCA1 and MCA2 were shown to be responsible for hypo-osmotic shock-induced increases in [Ca(2+) ]cyt . Thus, both proteins appear to be involved in the process of sensing mechanical stresses. We discussed the possible role of both proteins in sensing mechanical and gravitational stimuli.
植物的机械敏感通道可能感知由机械刺激（如触摸、风和膨压）以及重力刺激引起的张力增加。最近的研究已鉴定出细菌机械敏感通道MscS的植物同源物，该通道由膜张力门控，并通过从细菌细胞中释放小分子渗透物来降低细胞内渗透压。然而，这些同源物的生理作用尚未得到明确阐明，并且在拟南芥中只有其中两个被证明参与了对渗透胁迫下质体的保护。我们在拟南芥中鉴定出另一组机械敏感通道的候选物，命名为MCA1和MCA2，其同源物仅在植物基因组中发现。MCA1和MCA2分别由421和416个氨基酸残基组成，氨基酸序列具有73%的同源性，并且与任何已知的离子通道或转运蛋白都不同源。我们的结构研究表明，这两种蛋白质的N端区域（1至173个氨基酸）对于Ca(2+)内流活性是必要且充分的。有趣的是，该区域有一个推定的跨膜片段，含有一个Asp残基，其替代突变消除了这种活性。我们的生理学研究表明，根尖处表达的MCA1对于感知琼脂培养基或土壤的硬度是必需的。此外，MCA1和MCA2被证明负责低渗休克诱导的[Ca(2+)]cyt增加。因此，这两种蛋白质似乎都参与了感知机械应力的过程。我们讨论了这两种蛋白质在感知机械和重力刺激中的可能作用。
