Autophagy is activated and involved in cell death with participation of cathepsins during stress-induced microspore embryogenesis in barley

Microspores (小孢子) are reprogrammed towards embryogenesis by stress. Many microspores die after this stress, limiting the efficiency of microspore embryogenesis. Autophagy (自噬) is a degradation pathway (降解途径) that plays critical roles in stress response and cell death. In animals, cathepsins (组织蛋白酶) have an integral role in autophagy by degrading autophagic material; less is known in plants. Plant cathepsins are papain-like (类木瓜蛋白酶) C1A cysteine proteases (半胱氨酸蛋白水解酶) involved in many physiological processes (生理过程), including programmed cell death. We have analysed the involvement of autophagy in cell death, in relation to cathepsin activation, during stress-induced microspore embryogenesis in Hordeum vulgare (大麦). After stress, reactive oxygen species (ROS) and cell death increased and autophagy was activated, including HvATG5 and HvATG6 up-regulation and increase of ATG5, ATG8, and autophagosomes (自噬体). Concomitantly (并发地), cathepsin L/F-, B-, and H-like activities were induced, cathepsin-like genes HvPap-1 and HvPap-6 were up-regulated, and HvPap-1, HvPap-6, and HvPap-19 proteins increased and localized in the cytoplasm (细胞质), resembling (类似) autophagy structures. Inhibitors of autophagy and cysteine proteases reduced cell death and promoted embryogenesis. The findings reveal a role for autophagy in stress-induced cell death during microspore embryogenesis, and the participation (参与) of cathepsins. Similar patterns of activation, expression, and localization suggest a possible connection between cathepsins and autophagy. The results open up new possibilities to enhance microspore embryogenesis efficiency with autophagy and/or cysteine protease modulators.

小孢子在胁迫处理下会重编程进而胚胎发生。许多小孢子在胁迫处理后会直接死亡，限制了小孢子胚胎发生的效率。自噬是一种降解途径，其在胁迫响应和细胞死亡过程中扮演重要作用。在动物中，组织蛋白酶通过降解自噬材料在自噬过程中发挥着不可或缺的作用，然而对于其在植物中的作用还不清楚。植物的组织蛋白酶是一类类木瓜蛋白酶C1A半胱氨酸蛋白水解酶，该类酶参与许多的生理过程，包括程序性细胞死亡。本文分析了大麦小孢子在胁迫诱导下胚胎发生过程中自噬参与细胞死亡及与组织蛋白酶激活相关的过程。在胁迫处理后，活性氧物质和细胞死亡增加，并且自噬被激活，HvATG5和HvATG6基因上调表达，ATG5、ATG8和自噬体含量增加。同时，组织蛋白酶L/F、 B、和H类活性被诱导，组织蛋白酶类基因HvPap-1和HvPap-6上调表达，并且HvPap-1、HvPap-6和HvPap-19蛋白含量增加，定位于细胞质，类似于自噬结构。抑制自噬和组织蛋白酶会减少细胞死亡，同时促进胚胎发生。这些发现揭示了小孢子胚胎发生过程中自噬在胁迫诱导的细胞死亡中的作用，并且组织蛋白酶参与了这个过程。组织蛋白酶和自噬相似的激活、表达和定位模式表明这两者可能存在某种关联。本文的结果发现了通过自噬和组织蛋白酶的调节增强小孢子胚胎发生的新的可能性。

通讯：Pilar S. Testillano (http://autofagia.org/project/pilar-s-testillano/)

doi: https://doi.org/10.1093/jxb/erx455