Metabolic responses of Eucalyptus species to different temperature regimes

Species and hybrids of Eucalyptus are the world＇s most widely planted hardwood trees. They are cultivated across a wide range of latitudes and therefore environmen- tal conditions. In this context, comprehensive metabolo- mics approaches have been used to assess how different temperature regimes may affect the metabolism of three species of Eucalyptus, E. dunnii, E. grandis and E. pellita. Young plants were grown for 53 d in the greenhouse and then transferred to growth chambers at 10℃, 20℃ or 30℃ for another 7 d. In all three species the leaf chlorophyll content was positively correlated to temperature, and in E. pellita the highest temperature also resulted in a significant increase in stem biomass. Comprehensive metabolomics was performed using untargeted gas chromatography mass spectrometry （GC-MS） and liquid chromatography （LC）-MS. This approach enabled the comparison of the relative abundance of 88 polar primary metabolites from GC-MS and 625 semi-polar secondary metabolites from LC-MS. Using principal components analysis, a major effect of tempera- ture was observed in each species which was larger than that resulting from the genetic background. Compounds mostly affected by temperature treatment were subsequently selected using partial least squares discriminant analysis and were further identified. These putative annotations indicated that soluble sugars and several polyphenols, including tannins, triterpenes and alkaloids were mostly influenced.

Cellulose synthase ‘class specific regions’ are intrinsically disordered and functionally undifferentiated

Cellulose synthases （CESAs） are glycosyltransferases that catalyze formation of cellulose microfibrils in plant cell walls. Seed plant CESA isoforms cluster in six phylogenetic clades, whose non-interchangeable members play distinct roles within cellulose synthesis complexes （CSCs）. A ＇class specific region＇ （CSR）, with higher sequence similarity within versus between functional CESA classes, has been suggested to contribute to specific activities or interactions of different isoforms. We investigated CESA isoform specificity in the moss, Physcomitrella patens （Hedw.） B. S. G. to gain evolutionary insights into CESA structure/function relationships. Like seed plants, P. patens has oligomeric rosette-type CSCs, but the PpCESAs diverged independently and form a separate CESA clade. We showed that P. patens has two functionally distinct CESAs classes, based on the ability to complement the gametophore-negative phenotype of a ppcesa5 knockout line. Thus, non-interchangeable CESA classes evolved separately in mosses and seed plants. However, testing of chimeric moss CESA genes for complementation demonstrated that functional classspecificity is not determined by the CSR. Sequence analysis and computational modeling showed that the CSR is intrinsically disordered and contains predicted molecular recognition features, consistent with a possible role in CESA oligomerization and explaining the evolution of class-specific sequences without selection for class-specific function.