Adam Zach
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
Biochim Biophys Acta. 2015 Sep;1847(9):910-4. doi: 10.1016/j.bbabio.2014.12.006. Epub 2014 Dec 18.
Progress in the field of regulated intramembrane proteolysis (RIP) in recent years has not surpassed plant biology. Nevertheless, reports on RIP in plants, and especially in chloroplasts, are still scarce. Of the four different families of intramembrane proteases, only two have been linked to chloroplasts so far, rhomboids and site-2 proteases (S2Ps). The lack of chloroplast-located rhomboid proteases was associated with reduced fertility and aberrations in flower morphology, probably due to perturbations in jasmonic acid biosynthesis, which occurs in chloroplasts. Mutations in homologues of S2P resulted in chlorophyll deficiency and impaired chloroplast development, through a yet unknown mechanism. To date, the only known substrate of RIP in chloroplasts is a PHD transcription factor, located in the envelope. Upon proteolytic cleavage by an unknown protease, the soluble N-terminal domain of this protein is released from the membrane and relocates to the nucleus, where it activates the transcription of the ABA response gene ABI4. Continuing studies on these proteases and substrates, as well as identification of the genes responsible for different chloroplast mutant phenotypes, are expected to shed more light on the roles of intramembrane proteases in chloroplast biology.
近年来，膜内蛋白酶水解（RIP）领域的进展尚未超越植物生物学。然而，关于植物中RIP的报道，尤其是叶绿体中的RIP报道，仍然很少。在四种不同的膜内蛋白酶家族中，到目前为止只有两种与叶绿体有关，即类菱形蛋白酶和2型位点蛋白酶（S2P）。缺乏位于叶绿体的类菱形蛋白酶与育性降低和花形态异常有关，这可能是由于叶绿体中茉莉酸生物合成受到干扰所致。S2P同源物的突变通过一种尚不清楚的机制导致叶绿素缺乏和叶绿体发育受损。迄今为止，叶绿体中RIP唯一已知的底物是一种位于被膜的PHD转录因子。在被一种未知蛋白酶进行蛋白水解切割后，该蛋白的可溶性N端结构域从膜上释放出来并重新定位到细胞核，在那里它激活ABA反应基因ABI4的转录。对这些蛋白酶和底物的持续研究，以及对导致不同叶绿体突变表型的基因的鉴定，有望为膜内蛋白酶在叶绿体生物学中的作用提供更多的线索。
