OspTAC2 encodes a pentatricopeptide repeat protein and regulates rice chloroplast development

Functional chloroplast generation depends on the precise coordination of gene expression between the plastid and the nucleus and is essential for plant growth and development. In this study, a rice（Oryza sativa） mutant that exhibited albino and seedling-lethal phenotypes was isolated from a60Co-irradiated rice population. The mutant gene was identified as an ortholog of the Arabidopsis plastid transcriptionally active chromosome protein 2（p TAC2） gene, and the mutant strain was designated osptac2. Sequence and transcription analyses showed that Osp TAC2 encodes a putative chloroplast protein consisting of 10 pentratricopeptide repeat（PPR） domains and a C-terminal small Mut S-related（SMR） domain. Cytological observations via microscopy showed that the Osp TAC2-green fluorescent fusion protein is localized in the chloroplasts. Transmission electron microscopy revealed that the chloroplast of the osptac2 mutant lacks an organized thylakoid membrane. The transcript levels of all investigated PEP（plastid-encoded RNA polymerase）-dependent genes were dramatically reduced in the osptac2 mutant, whereas the transcript levels of NEP（nuclear-encoded polymerase）-dependent genes were increased. These results suggest that Osp TAC2 plays a critical role in chloroplast development and indicate that the molecular function of the Osp TAC2 gene is conserved in rice and Arabidopsis.

Characterization and molecular cloning of a serine hydroxymethyltransferase 1(OsSHM_1) in rice

Serine hydroxymethyltransferase (SHMT) is important for one carbon metabolism and photorespiration in higher plants for its participation in plant growth and development, and resistance to biotic and abiotic stresses. A rice serine hydroxymethyltransferase gene, OsSHM1, an ortholog of Arabidopsis SHM1, was isolated using map-based cloning. The osshm1 mutant had chlorotic lesions and a considerably smaller, lethal phenotype under natural ambient CO2 concentrations, but could be restored to wild type with normal growth under elevated CO2 levels (0.5% CO2), showing a typical photorespiratory phenotype. The data from antioxidant enzymes activity measurement suggested that osshm1 was subjected to significant oxidative stress. Also, OsSHM1 was expressed in all organs tested (root, culm, leaf, and young panicle) but predominantly in leaves. OsSHM1 protein is localized to the mitochondria. Our study suggested that molecular function of the OsSHM1 gene is conserved in rice and Arabidopsis.

LATERAL ROOTLESS2, a Cyclophilin Protein, Regulates Lateral Root Initiation and Auxin Signaling Pathway in Rice

Dear Editor, Cyclophilins （CYP） are a class of highly conserved pepti- dyl-prolyl cis-trans isomerases （PPlases） that play important roles in various biological processes in eukaryotes （reviewed in Romano et al. （2004））. In higher plants, a conserved sin- gle domain cyclophilin has been identified as a novel com- ponent of the auxin signaling pathway by analyzing the tomato diageotropica （dgt） mutant （Ivanchenko et al., 2006; Oh et al., 2006）. The dgt mutant displays a lateral-rootless and auxin-resistant phenotype （Ivanchenko et aL, 2006）. Further studies revealed that mutations in the DGT-like genes of Physcomitrella patens also exhibited an auxin-resistant phenotype, suggesting a conserved role of DGT-like proteins in auxin signaling. Moreover,