Cloning and Characterization of Genes Coding for Fructan Biosynthesis Enzymes (FBEs) in Triticeae Plants

Fructan is not only a carbon source for storage but also plays an important role as anti-stress agents in many plant species. Complex fructans having both β-(2,1)- and β-(2,6)-linked fructosyl units accumulate in Triticeae plants commonly. Three enzymes (sucrose: sucrose 1-fructosyltransferase, 1-SST, EC: 2.4.1.99; sucrose: fructan 6-fructosyltransferase, 6-SFT, EC: 2.4.1.10; and fructan: fructan 1-fructosyltransferase, 1-FFT, EC: 2.4.1.100) were involved in fructan biosynthesis in Triticeae plant species. We successfully isolated these genes from tetraploid wheat (Triticum turgidum, genotype: AABB), common wheat (Triticum aestivum L., genotype: AABBDD) and three wild relatives of common wheat, Triticum urartu Thum. (the origin of the AA genome), Aegilops speltoides (Tausch) Gren. (the putative source of the SS genome) and Aegilops tauschii Coss. (the source of the DD genome). Sequence analysis revealed that all the FBEs (fructan biosynthetic enzymes) had three highly conserved functional motifs except 1-SST (EU981912) from tetraploid wheat species only with conserved DPNG. Low pI (isoelectric point) and potential N-glycosylation sites were predicted, which were crucial for protein compartmentation and post-translational process. Analysis on subcelluar localization signals showed that only 6-SFT had vacuolar-directed signal. Sequences alignment result showed that 1-SST and 1-FFT were more conservative and had closer relationship each other, while 6-SFT was more active during the evolution processing. According to the syntenic relationship between wheat and rice genome, FBEs were predicated to be located on the homeologous group 6 and group 2 chromosomes. Expression profile confirmed that expression of all the three FBEs were drought-stress induced. This study can assist to establish a useful theoretical platform for cold- or drought-tolerant improvement of wheat by modulating FBEs expression.