AtRsmD Is Required for Chloroplast Development and Chloroplast Function in Arabidopsis thaliana.

AtRsmD was recently demonstrated to be a chloroplast 16S rRNA methyltransferase (MTase) for the m2G915 modification in Arabidopsis. Here, its function of AtRsmD for chloroplast development and photosynthesis was further analyzed. The AtRsmD gene is highly expressed in green photosynthetic tissues. AtRsmD is associated with the thylakoid in chloroplasts. The atrsmd-2 mutant exhibited impaired photosynthetic efficiency in emerging leaves under normal growth conditions. A few thylakoid lamellas could be observed in the chloroplast from the atrsmd-2 mutant, and these thylakoids were loosely organized. Knockout of the AtRsmD gene had minor effects on chloroplast ribosome biogenesis and RNA loading on chloroplast ribosomes, but it reduced the amounts of chloroplast-encoded photosynthesis-related proteins in the emerging leaves, for example, D1, D2, CP43, and CP47, which reduced the accumulation of the photosynthetic complex. Nevertheless, knockout of the AtRsmD gene did not cause a general reduction in chloroplast-encoded proteins in Arabidopsis grown under normal growth conditions. Additionally, the atrsmd-2 mutant exhibited more sensitivity to lincomycin, which specifically inhibits the elongation of nascent polypeptide chains. Cold stress exacerbated the effect on chloroplast ribosome biogenesis in the atrsmd-2 mutant. All these data suggest that the AtRsmD protein plays distinct regulatory roles in chloroplast translation, which is required for chloroplast development and chloroplast function.

[Effect of total knee arthroplasty under computer navigation on intraoperative blood loss and joint function recovery].

OBJECTIVE: To analyze the effect of computer navigation assisted total knee arthroplasty on intraoperative hemorrhage and postoperative joint function recovery in patients with knee osteoarthritis. METHODS: From February 2015 to December 2017, 65 patients with knee osteoarthritis treated by traditional total knee arthroplasty were retrospectively analyzed as the control group and 65 patients with knee osteoarthritis treated by total knee arthroplasty under computer navigation as the experimental group. Before operation, all patients showed red swelling pain of knee, pain of going up and down stairs, and pain and discomfort of waist when sitting up and standing up. All patients were treated with total knee arthroplasty. The control group was treated with traditional total knee arthroplasty, and the experimental group was treated with total knee arthroplasty under the computer navigation system. The operation related conditions of the two groups were recorded and compared including the operation time and hospitalization time; the changes of hemoglobin and hematocrit of the two groups were detected and compared before and 5 days after the operation; the blood loss of the two groups and the induced flow at each time point calculated and compared after the operation, and the perioperative allogeneic blood transfusion rate and average blood transfusion volume of the patients were recorded; The joint function scale (KSS) was used to evaluate the recovery of knee joint function before the operation, 6 and 18 months after the operation respectively and to record the incidence of postoperative infection, lower extremity venous thrombosis and other complications. RESULTS: All the patients were successfully operated and the prognosis of the wound was good. All the patients were followed up for an average of 18 months. The operation time of the experimental group was longer than that of the control group, and the hospitalization time was shorter than that of the control group (P <0.05) ; the KSS score of the two groups at each time point after operation was higher than that before operation, but the increasing range of the test group was higher than that of the control group (P<0.05) ; there was no significant difference between the two groups in the incidence of complications (P>0.05) . CONCLUSION: Under the guidance of computer navigation, total knee arthroplasty can prolong the operation time compared with single total knee arthroplasty, but it is more conducive to reduce perioperative blood loss, reduce the rate of postoperative allogeneic blood transfusion, ideal recovery of joint function, less complications, safety and reliability.

EMB2738, which encodes a putative plastid-targeted GTP-binding protein, is essential for embryogenesis and chloroplast development in higher plants.

In higher plants, chloroplasts carry out many important functions, and normal chloroplast development is required for embryogenesis. Numerous chloroplast-targeted proteins involved in embryogenesis have been identified. Nevertheless, their functions remain unclear. In this study, a chloroplast-localized protein, EMB2738, was reported to be involved in Arabidopsis embryogenesis. EMB2738 knockout led to defective embryos, and the embryo development in emb2738 was interrupted after the globular stage. Complementation experiments identified the AT3G12080 locus as EMB2738. Cellular observation indicated that severely impaired chloroplast development was observed in these aborted embryos. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis showed that chloroplast-encoded photosynthetic genes, which are transcribed by plastid-encoded RNA polymerase (PEP), are predominantly decreased in defective embryogenesis, compared with those in the wild-type. In contrast, genes encoding PEP core subunits, which are transcribed by nucleus-encoded RNA polymerase (NEP), were increased. These results suggested that the knockout of EMB2738 strongly blocked chloroplast-encoded photosynthesis gene expression in embryos. Silencing of the EMB2738 orthologue in tobacco through a virus-induced genome silencing technique resulted in an albinism phenotype, vacuolated chloroplasts and decreased PEP-dependent plastid transcription. These results suggested that NtEMB2738 might be involved in plastid gene expression. Nevertheless, genetic analysis showed that the NtEMB2738 coding sequence could not fully rescue the defective embryogenesis of the emb2738 mutant, which suggested functional divergence between NtEMB2738 and EMB2738 in embryogenesis. Taken together, these results indicated that both EMB2738 and NtEMB2738 are involved in the expression of plastid genes in higher plants, and there is a functional divergence between NtEMB2738 and EMB2738 in embryogenesis.

TAC7, an essential component of the plastid transcriptionally active chromosome complex, interacts with FLN1, TAC10, TAC12 and TAC14 to regulate chloroplast gene expression in Arabidopsis thaliana.

Transcriptionally active chromosome (TAC) is a fraction of protein/DNA complexes with RNA polymerase activity in the plastid. However, the function of most TAC proteins remains unknown. Here, we isolated two allelic mutants of the gene for a TAC component, TAC7, and performed functional analysis in plastid gene expression and chloroplast development in Arabidopsis. tac7-1 is a mutant with a premature translation termination isolated from a population treated with ethyl methane sulfonate, and tac7-2 is a transfer-DNA tagging mutant. Both of them showed an albino phenotype when grown under normal light conditions, and a few appressed membranes were observed inside the defective chloroplasts. These data indicate that TAC7 is important for thylakoid biogenesis. The TAC7 gene encodes an uncharacterized 161 amino acids polypeptide localized in chloroplast. The transcriptional levels of plastid-encoded polymerase (PEP)-dependent genes were downregulated in tac7-2, suggesting that PEP activity was decreased in the mutant. Yeast two-hybrid assay shows that TAC7 can interact with the four TAC components including FLN1, TAC10, TAC12 and TAC14 which are involved in redox state changes, phosphorylation processes and phytochrome-dependent light signaling, respectively, These data indicate that TAC7 plays an important role for TAC to regulate PEP-dependent chloroplast gene expression and chloroplast development.