Transcriptional regulation of thylakoid galactolipid biosynthesis coordinated with chlorophyll biosynthesis during the development of chloroplasts in Arabidopsis.

Biogenesis of thylakoid membranes in chloroplasts requires the coordinated synthesis of chlorophyll and photosynthetic proteins with the galactolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), which constitute the bulk of the thylakoid lipid matrix. MGD1 and DGD1 are the key enzymes of MGDG and DGDG synthesis, respectively. We investigated the expression profiles of MGD1 and DGD1 in Arabidopsis to identify the transcriptional regulation that coordinates galactolipid synthesis with the synthesis of chlorophyll and photosynthetic proteins during chloroplast biogenesis. The expression of both MGD1 and DGD1 was repressed in response to defects in chlorophyll synthesis. Moreover, these genes were downregulated by norflurazon-induced chloroplast malfunction via the GENOMES-UNCOUPLED1-mediated plastid signaling pathway. Similar to other photosynthesis-associated nuclear genes, the expression of MGD1 and DGD1 was induced by light, in which both cytokinin signaling and LONG HYPOCOTYL5-mediated light signaling played crucial roles. The expression of these galactolipid-synthesis genes, and particularly that of DGD1 under continuous light, was strongly affected by the activities of the GOLDEN2-LIKE transcription factors, which are potent regulators of chlorophyll synthesis and chloroplast biogenesis. These results suggest tight transcriptional coordination of galactolipid synthesis with the formation of the photosynthetic chlorophyll-protein complexes during leaf development. Meanwhile, unlike the photosynthetic genes, the galactolipid synthesis genes were not upregulated during chloroplast biogenesis in the roots, even though the galactolipids accumulated with chlorophylls, indicating the importance of post-transcriptional regulation of galactolipid synthesis during root greening. Our data suggest that plants utilize complex regulatory mechanisms to modify galactolipid synthesis with chloroplast development during plant growth.

Regulation of root greening by light and auxin/cytokinin signaling in Arabidopsis.

Tight coordination between plastid differentiation and plant development is best evidenced by the synchronized development of photosynthetic tissues and the biogenesis of chloroplasts. Here, we show that Arabidopsis thaliana roots demonstrate accelerated chlorophyll accumulation and chloroplast development when they are detached from shoots. However, this phenomenon is repressed by auxin treatment. Mutant analyses suggest that auxin transported from the shoot represses root greening via the function of indole-3-acetic acid14, auxin response factor7 (ARF7), and ARF19. Cytokinin signaling, on the contrary, is required for chlorophyll biosynthesis in roots. The regulation by auxin/cytokinin is dependent on the transcription factor long hypocotyl5 (HY5), which is required for the expression of key chlorophyll biosynthesis genes in roots. The expression of yet another root greening transcription factor, golden2-like2 (GLK2), was found to be regulated in opposing directions by auxin and cytokinin. Furthermore, both the hormone signaling and the GLK transcription factors modified the accumulation of HY5 in roots. Overexpression of GLKs in the hy5 mutant provided evidence that GLKs require HY5 to maximize their activities in root greening. We conclude that the combination of HY5 and GLKs, functioning downstream of light and auxin/cytokinin signaling pathways, is responsible for coordinated expression of the key genes in chloroplast biogenesis.

Triacylglycerol deposition with group IVC phospholipase A2 expression in oleate- and linoleate-stimulated Huh-7 hepatocytes.

The accumulation of hepatocellular triacylglycerol (TG), a major symptom of fatty liver, is associated with the excessive incorporation of exogenous free fatty acids into hepatocytes, the free fatty acids inducing an increase in TG bearing acyl chains derived from not only themselves but also endogenous fatty acids. However, the mechanisms responsible for the supply of endogenous fatty acids, which are mainly esterified into phospholipids, remain unclear. In the present study, we examined the possible involvement of intracellular phospholipase A(2) (PLA(2))s including group IVA, IVC, VIA, and VIB PLA(2)s, which catalyze the release of endogenous fatty acids, in the deposition of TG in hepatocytes. Stimulation of human hepatoma Huh-7 cells with oleate or linoleate for 48 h increased TG contents time-dependently. Under the conditions, increased expression of group IVC PLA(2) mRNA and protein was observed at 6-12 h and 24-48 h after the stimulation, respectively. However, mRNA levels of group IVA, VIA, or VIB PLA(2) did not change. When cells were treated with methyl arachidonyl fluorophosphonate used as an inhibitor of group IVC PLA(2), the fatty acid-induced deposition of TG was partially but significantly suppressed at 48 h, although no significant inhibition was observed at 24 h. Overexpression of wild-type group IVC PLA(2) but not a catalytically inactive mutant of group IVC PLA(2) tended to increase cellular TG levels. The present findings suggest that stimulation of Huh-7 hepatocytes with free fatty acids induces the expression of group IVC PLA(2), which is involved in the fatty acid-induced deposition of TG.

Involvement of auxin signaling mediated by IAA14 and ARF7/19 in membrane lipid remodeling during phosphate starvation.

In higher plants, phosphate (Pi) deficiency induces the replacement of phospholipids with the nonphosphorous glycolipids digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG). Genes involved in membrane lipid remodeling are coactivated in response to Pi starvation, but the mechanisms that guide this response are largely unknown. Previously, we reported the importance of auxin transport for DGDG accumulation during Pi starvation. To understand the role of auxin signaling in Arabidopsis membrane lipid remodeling, we analyzed slr-1, a gain-of-function mutant of IAA14 (a repressor of auxin signaling), and arf7arf19, a loss-of-function mutant of auxin response factors ARF7 and ARF19. In slr-1 and arf7arf19, Pi stress-induced accumulation of DGDG and SQDG was suppressed. Reduced upregulation of glycolipid synthase and phospholipase genes in these mutants under Pi-deficient conditions indicates that IAA14 and ARF7/19 affect membrane lipid remodeling at the level of transcription. Pi stress-dependent induction of a non-protein-coding gene, IPS1, was also lower in slr-1 and arf7arf19, whereas expression of At4 (another Pi stress-inducible non-protein-coding gene), anthocyanin accumulation, and phosphodiesterase induction were not reduced in the shoot. High free Pi content was observed in slr-1 and arf7arf19 even under Pi-deficient conditions, suggesting that Pi homeostasis during Pi starvation is altered in these mutants. These results demonstrate a requirement of auxin signaling mediated by IAA14 and ARF7/19 for low-Pi adaptation in Arabidopsis.

Mortality rate of patients with asymptomatic primary biliary cirrhosis diagnosed at age 55 years or older is similar to that of the general population.

PURPOSE: Recent routine testing for liver function and anti-mitochondrial antibodies has increased the number of newly diagnosed patients with primary biliary cirrhosis (PBC). This study investigated the prognosis of asymptomatic PBC patients, focusing on age difference, to clarify its effect on the prognosis of PBC patients. METHODS: The study was a systematic cohort analysis of 308 consecutive patients diagnosed with asymptomatic PBC. We compared prognosis between the elderly (55 years or older at the time of diagnosis) and the young patients (<55 years). The mortality rate of the patients was also compared with that of an age- and gender-matched general population. RESULTS: The elderly patients showed a higher aspartate aminotransferase-to-platelet ratio, and lower alanine aminotransferase level than the young patients (P < 0.01 and P = 0.03, respectively). The two groups showed similar values for alkaline phosphatase and immunoglobulin M. Death in the young patients was more likely to be due to liver failure (71%), while the elderly were likely to die from other causes before the occurrence of liver failure (88%; P < 0.01), especially from malignancies (35%). The mortality rate of the elderly patients was not different from that of the age- and gender-matched general population (standardized mortality ratio, 1.1; 95% confidence interval, 0.6-1.7), although this rate was significantly higher than that of the young patients (P = 0.044). CONCLUSIONS: PBC often presents as more advanced disease in elderly patients than in the young. However, the mortality rate of the elderly patients is not different from that of an age- and gender-matched general population.

Clinicopathological features of acute-onset autoimmune hepatitis.

The clinicopathological features of nine acute-onset autoimmune hepatitis (AIH) patients were compared with those of 29 classical AIH patients. The clinical features of acute-onset AIH showed significantly higher serum ALT levels, lower serum IgG levels and AIH score than those of classical AIH, although the type of auto-antibodies, age and gender were not different between the two groups. Pathological features showed that the stages of acute-onset AIH varied from stage 1 to stage 4 and were less advanced compared with those of classical AIH. One patient showed submassive hepatic necrosis. Both centrilobular necrosis and interface hepatitis were observed in 7 and 8 of 9, respectively. Three stage 1 patients with centrilobular necrosis and one patient with submassive hepatic necrosis were suggestive of acute presentation, while patients with stages 2 and 4 fibrosis were suggestive of acute exacerbation of chronic disease. An immunohistochemical study demonstrated that CD8 T cells were predominant at both interface hepatitis and centrilobular necrosis, while CD79alpha-positive B lineage cells were predominant at interface hepatitis. These results suggest that acute-onset AIH includes both acute presentation and acute exacerbation of chronic disease and that centrilobular necrosis might be a prevailing pathological feature.