A Preliminary Research On The Programmed Cell Death Regulated By Plant LrgB Homologous Genes

Programmed cell death(PCD) plays a vital role in the life cycle of various organisms. It is reported that there are three types of PCD in animals:apoptosis, autophagy and necrosis; among which mitochondria plays a vital role by controling the permeability of the membrane. While the regulation of bacterial lysis is commanded by the cidAB/lrgAB system, which can control the release of muramidase and then manipulate the fate of a bacterial cell.Previously, we have showed that there is a homologous gene of bacterial lrgAB in Arabidopsis thaliana, which have evolved into two domains of a single gene via the result of topo prediction. As the conservation of LrgB is higher than that of LrgA between plant and bacteria, so it was named as LrgB. It is reported that AtLrgB is involved in the regulation of chloroplast fuction, and highly related to the development of leaf, even the initiation of cell death. Except that, AtLrgB also has a hand in the partition of carbon assimilation, modulating the metabolic balance of sucrose and starch.The present research is started from the sequences blast of plant LrgB homologues, which informed that there ubiquitously exist LrgB homologues in plant, and their evolution follow that of the pattern in Vegetabilia. It is interesting that there are two LrgB homologues in some plant, among of which we can find some similarity of their domains and subcellular localization. In our experiments, the LrgB homologues of Physcomitrella patens, Selaginella moellendorfi and Oryza sativa are expressed separately in Arabidopsis thaliana, which arouse the growth restrain as small and pale leaf, hypocotyl shortening. Fluorescence localization of their protein products shows that they are localized at chloroplast at the stage of growth period, following which the conservative one are found at the plasma membrane along with the trigger of cell death. All of this offer a strong argument of the involvement of plant LrgB homologues in cell death. The difference with Arabidopsis thaliana is that the LrgB homologues of those plants are all expressed at all of organizations and stages, fully confirming that those genes not only played a part in regulating the fuction of chloroplasts, but also they are important in the life cycle of plants.At the same time, expression of PpLrgB in Escherichia coli lead to the inhibition of cell division and biofilm development, and the strengthen of resistance to ampicillin. Those all implying that PpLrgB retarded the division of bacterial cells, as well as the lysis of them. We speculate that overexpression of PpLrgB ruins the balance of bacterial cid/lrg system that regulating cell death and lysis, and then it keeps the bacterial cell from continous dividing or dying. Moreover, overexpression of PpLrgB in E. coli also have an effect on its growth condition either in oxidative stress environment or in glucose medium. Those fuctions share the similarity with the bacterial cidAB/lrgAB system, informing that plant LrgB dedicated to cell death regulation is undoubtable.