Cloning and characterization of a putative fructosyltransferase and two putative invertase genes from the temperate grass Lolium temulentum L.

The invertases of Lolium temulentum have been characterized at the enzyme level. However, studies on the expression of the genes coding for these enzymes have been lacking. To elucidate the role of acid 'invertase-like' genes in sucrose metabolism and carbon partitioning in Gramineae further, three 'invertase-like' homologous clones were isolated from L. temulentum cDNA expression libraries based on leaf tissue, using maize soluble invertase probes. The effect of developmental stage and alterations in carbohydrate status on the expression and tissue distribution of these genes was investigated. The three highly homologous genes (Inv 1:2, Inv 1:4, and FT 2:2) show different patterns of expression and different tissue distribution. Inv 1:2 was predominantly expressed in root tissue. Expression increased during the dark in root and tiller base tissue. Minimal variations in gene expression were observed in leaf tissue following changes in carbohydrate status. Inv 1:4 was predominantly expressed in tiller bases, leaf sheath, and leaf base, with increased expression in tissue samples in the dark period. FT 2:2 was also predominantly expressed in tiller bases, leaf sheath, and leaf base. Higher expression was observed in leaf tissue following increases in carbohydrate content, in a manner that paralleled the regulation and spatial occurrence of fructan in the leaf tissue. Whilst invertases and fructosyltransferases are difficult to distinguish at the level of the whole sequence, analysis of 5' sequence and specific amino acids allows discrimination which correlates with patterns of expression within the tissue. Based on expression patterns and sequence characteristics, it is proposed that Inv 1:2 and Inv 1:4 code for soluble acid invertases, whilst FT 2:2 codes for a fructosyltransferase.