Sueldo Daniela J, van der Hoorn Renier A L
The Plant Chemetics Laboratory, Department of Plant Sciences, University of Oxford, UK.
FEBS J. 2017 May;284(10):1577-1585. doi: 10.1111/febs.14034. Epub 2017 Feb 26.
Caspases are key regulators of apoptosis in animals. This correlation has driven plant researchers for decades to look for caspases regulating programmed cell death (PCD) in plants. These studies revealed caspase-like activities, caspase-related proteases, and cysteine (Cys) proteases regulating PCD in plants, but identified no caspases and no conserved, apoptosis-like death pathway. Here, we critically review the evidence for Cys proteases implicated in PCD in plants. We discuss the role of papain-like Cys proteases, vacuolar processing enzymes, and metacaspases in PCD during the development of tracheary elements, seed coat, suspensor, and tapetum, and during the hypersensitive response. There are several convincing cases where these Cys proteases are required for PCD, but this requirement is often not conserved across different plant species. There are also cases where Cys proteases contribute to the speed, but not the timing of PCD, while other Cys proteases are nonessential for PCD, but have other roles, e.g., in the clearance of cell remains after PCD. These data illustrate the need for caution when generalizing the role of Cys proteases in regulating PCD in plants, and call for studies that further investigate plant Cys proteases and other PCD regulators.
半胱天冬酶是动物细胞凋亡的关键调节因子。几十年来，这种关联促使植物研究人员寻找调节植物程序性细胞死亡（PCD）的半胱天冬酶。这些研究揭示了植物中调节PCD的类半胱天冬酶活性、半胱天冬酶相关蛋白酶和半胱氨酸（Cys）蛋白酶，但未鉴定出半胱天冬酶，也未发现保守的、类似凋亡的死亡途径。在此，我们批判性地回顾了与植物PCD相关的Cys蛋白酶的证据。我们讨论了木瓜蛋白酶样Cys蛋白酶、液泡加工酶和 metacaspases在管状分子、种皮、胚柄和绒毡层发育过程中以及过敏反应期间PCD中的作用。有几个令人信服的案例表明这些Cys蛋白酶是PCD所必需的，但这种需求在不同植物物种中往往并不保守。也有一些案例表明，Cys蛋白酶有助于PCD的速度，但不影响其时间，而其他Cys蛋白酶对PCD并非必需，但具有其他作用，例如在PCD后清除细胞残骸。这些数据表明，在概括Cys蛋白酶在调节植物PCD中的作用时需要谨慎，并呼吁开展进一步研究植物Cys蛋白酶和其他PCD调节因子的研究。
