Abstract
BackgroundVacuolar processing enzymes (VPEs) have been identified as the enzymes that regulate vacuole-mediated programmed cell death (PCD) in plants. The mechanism that VPE regulates the PCD in rice aleurone layers remains unknown.ResultsThe aleurone layers treated with distilled water exerted caspase-1 and VPE activity, both of which were inhibited by the caspase-1 specific inhibitor Ac-YVAD-CMK but not by the caspase-3 specific inhibitor Ac-DEVD-CHO. However, the caspase-1 and caspase-3 inhibitors weakened the activity of caspase-3. Combined with the effects of endogenous gibberellin (GA) on the induction of OsVPEs, we suggest that the OsVPE3 in the aleurone layers, which exhibits caspase-1-like activity, is a key molecule in GA-induced PCD via regulating the protease with caspase-3-like activity. Many studies have confirmed that vacuolar fusion is an important feature of vacuole-mediated PCD in plants. In this experiment, the process of vacuole fusion was accompanied by changes in the structure of actin filaments (AFs), specifically, their depolymerization and polymerization. The process of vacuolar fusion was accelerated or delayed by the promotion or inhibition of the depolymerization of AFs, respectively. Here, the inhibition of OsVPE3 blocked the depolymerization of AFs and delayed the fusion of vacuoles, indicating that OsVPE3 can regulate the fusion of vacuoles in rice aleurone layers via mediating AFs. Furthermore, the depolymerization of AFs contributed to the up-regulation of OsVPE3 gene expression and VPE activity, resulting in accelerated PCD in rice aleurone layers. However, the inhibitor of VPE reversed the effects of AF depolymerization on the activity of VPE, then postponing the process of PCD, implying that AF can involve in GA-induced PCD of rice aleurone layers by mediating OsVPE3.ConclusionsTogether, activation of OsVPE3 and depolymerization of AFs shortened the process of vacuolation and PCD in rice aleurone layers, and OsVPE3 interacted with AFs during regulation.
Highlights
Vacuolar processing enzymes (VPEs) have been identified as the enzymes that regulate vacuole-mediated programmed cell death (PCD) in plants
OsVPE3 Exhibits Specific Caspase-1-like Activity in Rice Aleurone Layers To analyze the protease property of VPE, we examined the activities of VPE, caspase-1- and caspase-3-like in aleurone layers treated with the inhibitors of caspase-1 and caspase-3
Zhang et al (2018) detected the levels of OsVPE1-4 gene expression in the intact seeds imbibed for 12 h and in the aleurone layers, embryos, and endosperm of the intact seeds imbibed for 12 h, the results revealed that the transcription level of OsVPE3 was much higher than these of OsVPE1, OsVPE2, and OsVPE4 in the intact seeds, aleurone layers, and embryos
Summary
Vacuolar processing enzymes (VPEs) have been identified as the enzymes that regulate vacuole-mediated programmed cell death (PCD) in plants. Studies have shown that VPE exerts caspase-1-like activity in the vacuole-induced cell death of TMV (tobacco mosaic virus) in Nicotiana (Hatsugai et al, 2004), and that Ac-ESEN-CHO, a specific inhibitor of VPE, effectively inhibits the occurrence of PCD (Hatsugai et al, 2009; Li et al, 2012). Pharmacology experiments showed that specific inhibitors of caspase-1 and caspase-3, Ac-YVAD-CHO and Ac-DEVD-CHO, prevent the DNA strand breaks and the degradation of PARP, postponing the occurrence of menadione-induced PCD in tobacco protoplasts (Sun et al, 1999) Both Ac-YVAD-CMK and Ac-DEVD-CHO have already been shown to inhibit PCD of rice aleurone layers at 100 μM (Zheng et al, 2017). Other studies clarified that inhibition of OsVPE3 expression reduces the rupture of vacuoles, leading to improved tolerance of rice stomata to salt in the development (Lu et al, 2016)
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