Is Critical for Chloroplast Development in Leaf Epidermal Guard Cells.

In , the () gene encodes a thylakoid membrane-localized protease involved in chloroplast development in leaf mesophyll cells. Recently, was also found to be crucial for the maintenance of grana in mesophyll chloroplasts. To further explore the function of in leaf tissues, we examined the phenotype of chloroplasts in the leaf epidermal guard cells and pavement cells of two Ar irradiation-derived mutants, Ar50-33-pg1 and . Fluorescence microscopy revealed that fully expanded leaves of both mutants showed severe chlorophyll deficiency in both epidermal cell types. Guard cells in the mutant exhibited permanent defects in chloroplast formation during leaf expansion. Labeling of plastids with CaMV or () promoter-driven stroma-targeted fluorescent proteins revealed that guard cells contained the normal number of plastids, but with moderately reduced size, compared with wild-type guard cells. Transmission electron microscopy further revealed that the development of thylakoids was impaired in the plastids of mutant guard mother cells, guard cells, and pavement cells. Collectively, these observations demonstrate that is involved in chloroplast formation in the leaf epidermis and is particularly critical for chloroplast differentiation in guard cells.