Yoshimasa Tsujii

OsMYC2 mediates numerous defence-related transcriptional changes via jasmonic acid signalling in rice

Jasmonic acid (JA) plays central roles in various events in plants, especially defence against pathogens and insects. The basic helix-loop-helix (bHLH) transcription factor MYC2 has attracted attention as a master regulator of JA signalling in dicotyledonous plants. However, how MYC2 functions in monocotyledonous plants, including agriculturally important crops such as cultivated rice, has been poorly understood. To elucidate the comprehensive effects of rice MYC2 (OsMYC2) on the JA-inducible transcriptional modifications, we performed RNA-sequencing by using OsMYC2-knockdown plants (osmyc2RNAi). In osmyc2RNAi, JA-inducible expression of many defence-related genes, for example chitinases and proteinase inhibitors, was compromised. Decrease in JA-dependent activation of the biosynthetic pathways of specialised metabolites, especially defence compounds, was also evident in the osmyc2RNAi line. Furthermore, a substantial change was noted in the expression of distinct types of transcription factors, such as MYB-type factors, likely depicting the importance of OsMYC2 in not only defence responses but also other morphogenetic events. Our findings provide fundamental information to understand the overall functions of MYC2 in JA signalling in monocotyledonous plants, which might yield agricultural benefits.

mTOR inhibition by rapamycin increases ceramide synthesis by promoting transforming growth factor‐β1/Smad signaling in the skin

Although mammalian target of rapamycin (mTOR) mediates a wide variety of biological functions, little information is available on the effect of mTOR on the functions of skin cells. In this study, we investigated effects of mTOR inhibition by rapamycin on ceramide synthesis in the skin of rats and human keratinocytes and its regulatory mechanisms. The phosphorylation of p70 S6 kinase, which indicates mTOR activation, was induced in the skin of rats fed a high‐fat diet, but this abnormality was reversed by supplementation with rapamycin. Ceramide levels and the mRNA levels of serine palmitoyltransferase (SPT) and transforming growth factor (TGF)‐β1 were suppressed in the skin of rats fed high‐fat diets, but this abnormality was reversed by supplementation with rapamycin. TGF‐β1‐induced SPT mRNA expression was blocked by SB525334, an inhibitor of TGF‐β1‐induced Smad2/3 nuclear localization, in human keratinocytes. Rapamycin‐induced SPT mRNA expression was blocked by an anti‐TGF‐β1 antibody or SB525334 in human keratinocytes. These results show that mTOR inhibition by rapamycin increases ceramide synthesis by promoting TGF‐β1/Smad signaling in the skin.

Effects of Cultivar and Cultivation Region on Endosperm Enzyme Activity Involved in the Palatability of Cooked Rice

The endosperm enzyme activity of rice is thought to vary depending on various parameters such as cultivar type, storage conditions, and cultivation region. Focusing on the variation in enzyme activity, we examined the relationship between these parameters and the palatability of cooked rice. To improve measurement convenience, rapidity, substrate specificity and sensitivity, enzyme activity was assessed using synthetic substrates. The following enzymes were examined and subjected to chemometric analysis : αand β -amylases; α-glucosidase; β glucanase; β -galactosidase; α -mannosidase; and β -xylanase. The results indicated that the endosperm enzyme activities differed among cultivars closely related to Koshihikari, namely, activities of α and β -amylase and β galactosidase differed significantly between cultivars. _Pirouette` multivariate analysis software was used to perform principal component analysis and thereby group cultivars according to endosperm enzyme activity. Haenuki was grouped closely to Koshihikari, whereas Kirara 397 was distantly related to Koshihikari. We were able to correlate carbohydrate-related enzyme activity with the characteristics of the cultivars. (Received Jul. 8, 2014 ; Accepted Oct. 15, 2014)

Metabolic abnormalities induced by mitochondrial dysfunction in skeletal muscle of the renal carcinoma Eker (TSC2+/−) rat model

Tuberous sclerosis complex 2 (TSC2) is a mediator of insulin signal transduction, and a loss of function in TSC2 induces hyperactivation of mTORC1 pathway, which leads to tumorigenesis. We have previously demonstrated that Eker rat model, which is heterozygous for a TSC2 mutation, exhibits hyperglycemia and hyperketonemia. The present study was to investigate whether these changes also can affect metabolism in skeletal muscle of the Eker rat. Wild-type (TSC2+/+) and Eker (TSC2+/−) rats underwent an oral glucose tolerance test, and the latter showed decrease in whole-body glucose utilization. Additionally, reductions in the expression of glycolysis-, lipolysis-, and ketone body-related genes in skeletal muscle were observed in Eker rats. Furthermore, ATP content and mitochondrial DNA copy number were lower in skeletal muscle of Eker rats. These data demonstrate that heterozygous to mutation TSC2 not only affects the liver metabolism, but also skeletal muscle metabolism, via mitochondrial dysfunction. Graphical abstract Eker rats exhibit glucose intolerance due to the inhibition of glucose uptake at the skeletal muscle, which was explained by low number and dysfunction of mitochondria.