Trehalose metabolism in Arabidopsis: occurrence of trehalose and molecularcloning and characterization of trehalose-6-phosphate synthase homologues

Axenically grown Arabidopsis thaliana plants were analysed for the occurren ce of trehalose. Using gas chromatography-mass spectrometry (GC-MS) analysi s, trehalose was unambiguously identified in extracts from Arabidopsis infl orescences. In a variety of organisms, the synthesis of trehalose is cataly sed by trehalose-6-phosphate synthase (TPS; EC 2.4.1.15) and trehalose-6-ph osphate phosphatase (TPP; EC 3.1.3.12). Based on EST (expressed sequence ta g) sequences, three full-length Arabidopsis cDNAs whose predicted protein s equences show extensive homologies to known TPS and TPP proteins were ampli fied by RACE-PCR. The expression of the corresponding genes, AtTPSA, AtTPSB and AtTPSC, and of the previously described TPS gene, AtTPS1, was analysed by quantitative RT-PCR. All of the genes were expressed in the rosette lea ves, stems and flowers of Arabidopsis plants and, to a lower extent, in the roots. To study the role of the Arabidopsis genes, the AtTPSA and AtTPSC c DNAs were expressed in Saccharomyces cerevisiae mutants deficient in trehal ose synthesis. In contrast to AtTPS1, expression of AtTPSA and AtTPSC in th e tps1 mutant lacking TPS activity did not complement trehalose formation a fter heat shock or growth on glucose. In addition, no TPP function could be identified for AtTPSA and AtTPSC in complementation studies with the S. ce revisiae tps2 mutant lacking TPP activity. The results indicate that while AtTPS1 is involved in the formation of trehalose in Arabidopsis, some of th e Arabidopsis genes with homologies to known TPS/TPP genes encode proteins lacking catalytic activity in trehalose synthesis.