Swammerdam Institute for Life Sciences, section Plant Physiology, University of Amsterdam, Science Park 904, Amsterdam, 1098 XH, The Netherlands.
Swammerdam Institute for Life Sciences, section Plant Cell Biology, University of Amsterdam, Science Park 904, Amsterdam, 1098 XH, The Netherlands.
Plant Cell Physiol. 2018 Mar 1;59(3):469-486. doi: 10.1093/pcp/pcx194.
Phospholipase C (PLC) is well known for its role in animal signaling, where it generates the second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG), by hydrolyzing the minor phospholipid, phosphatidylinositol 4,5-bisphosphate (PIP2), upon receptor stimulation. In plants, PLC's role is still unclear, especially because the primary targets of both second messengers are lacking, i.e. the ligand-gated Ca2+ channel and protein kinase C, and because PIP2 levels are extremely low. Nonetheless, the Arabidopsis genome encodes nine PLCs. We used a reversed-genetic approach to explore PLC's function in Arabidopsis, and report here that PLC3 is required for proper root development, seed germination and stomatal opening. Two independent knock-down mutants, plc3-2 and plc3-3, were found to exhibit reduced lateral root densities by 10-20%. Mutant seeds germinated more slowly but were less sensitive to ABA to prevent germination. Guard cells of plc3 were also compromised in ABA-dependent stomatal closure. Promoter-β-glucuronidase (GUS) analyses confirmed PLC3 expression in guard cells and germinating seeds, and revealed that the majority is expressed in vascular tissue, most probably phloem companion cells, in roots, leaves and flowers. In vivo 32Pi labeling revealed that ABA stimulated the formation of PIP2 in germinating seeds and guard cell-enriched leaf peels, which was significantly reduced in plc3 mutants. Overexpression of PLC3 had no effect on root system architecture or seed germination, but increased the plant's tolerance to drought. Our results provide genetic evidence for PLC's involvement in plant development and ABA signaling, and confirm earlier observations that overexpression increases drought tolerance. Potential molecular mechanisms for the above observations are discussed.
磷脂酶 C（PLC）在动物信号转导中因其水解次要磷脂磷脂酰肌醇 4,5-二磷酸（PIP2）生成第二信使肌醇 1,4,5-三磷酸（IP3）和二酰基甘油（DAG）而广为人知。在植物中，PLC 的作用仍不清楚，特别是因为缺少两种第二信使的主要靶标，即配体门控 Ca2+通道和蛋白激酶 C，并且因为 PIP2 水平极低。尽管如此，拟南芥基因组编码了九个 PLC。我们使用反向遗传学方法探索了 PLC 在拟南芥中的功能，并在此报告 PLC3 对于正常的根系发育、种子萌发和气孔开放是必需的。发现两个独立的敲低突变体 plc3-2 和 plc3-3 的侧根密度降低了 10-20%。突变体种子萌发更慢，但对 ABA 更不敏感以防止萌发。plc3 的保卫细胞也在 ABA 依赖的气孔关闭中受到损害。启动子-β-葡萄糖醛酸酶（GUS）分析证实 PLC3 在保卫细胞和萌发种子中表达，并表明大部分在根部、叶片和花朵的维管束组织中表达，很可能是韧皮部伴胞。体内 32Pi 标记显示 ABA 刺激萌发种子和富含保卫细胞的叶皮中 PIP2 的形成，而在 plc3 突变体中显著减少。PLC3 的过表达对根系结构或种子萌发没有影响，但增加了植物对干旱的耐受性。我们的结果为 PLC 参与植物发育和 ABA 信号转导提供了遗传证据，并证实了早期的观察结果，即过表达增加了干旱耐受性。讨论了上述观察结果的潜在分子机制。
