The Function Of Two Chloroplast-targeted Proteins-FtsHL3 And FtsHL5 In Embryogenesis In Arabidopsis

Chloroplast biogenesis is tightly linked with embryogenesis and seedling development. A growing bulk of work has been done on the molecular mechanisms underlying chloroplast development and function; however, the molecular mechanisms involved in chloroplast biogenesis during embryogenesis and their relationship remain unclear. Chloroplasts first accumulate at the heart stage during embryogenesis in Arabidopsis. Several FtsH(Filamentation temperature-sensitive H) proteases have been reported to be important for chloroplast biogenesis and thylakoid maintenance in Arabidopsis. There are five FtsH-like (FtsHL) genes which encode the polypeptides containing no Zn-binding motifs, unlike FtsHs, in Arabidopsis genome. To date, none of the FtsHL genes has been described for its function in plants.In this study, we isolate the Arabidopsis T-DNA insertion mutants of FtsHL3 and FtsHL5, two Arabidopsis FtsHL genes, respectively, thus named ftshl3 and ftshl5.We show that both of the mutants are severely defective in embryo development with the globular to heart transition stage arrested, thus leading to embryo lethality. Transmission electron microscopic analysis reveals the absence of normal chloroplast development in the mutant embryos with a failure to form thylakoids. Subcelluar localization study with western blot using antiFtsHL3 and antiFtsHL5 antibodies shows that FtsHL3 and FtsHL5 proteins are localized in the chloroplast thylakoid membrane. FtsHL3 can interact with FtsHL5 in yeast cells, suggesting that these two proteins may form a protein complex to control chloroplast thylakoid formation. These above mentioned results indicate that FtsHL3 and FtsHL5 are involved in chloroplast biosynthesis during embryogenesis in Arabidopsis.