Transcript profiling of fructan biosynthetic pathway genes reveals association of a specific fructosyltransferase isoform with the high sugar trait in Lolium perenne

Abstract

Lolium perenne cultivars with elevated levels of fructans in leaf blades (high sugar-content grasses) have been developed to improve animal nutrition and reduce adverse environmental impacts of pastoral agricultural systems. Expression of the high sugar trait can vary substantially depending on genotype×environment (G×E) interactions. We grew three potential high sugar-content and a control cultivar in three temperature regimes and quantified water soluble carbohydrates (WSCs) and the expression of all functionally characterised L. perenne fructan pathway genes in leaf tissues. We also analysed the distribution, expression and sequence variation of two specific isoforms of Lp6G-FFT (fructan: fructan 6G-fructosyltransferase). Our study confirmed a significant G×E interaction affecting the accumulation of fructans in the high sugar-content cultivar AberDart, which accumulated higher levels of high DP (degree of polymerisation) fructans in blades compared to the control cultivar only when grown at 20°C (day)/10°C (night) temperatures. The cultivar Expo on the other hand accumulated significantly higher levels of high DP fructans in blades independent of temperature. Fructan levels in pseudostems were higher than in blades, and they increased markedly with decreasing temperature, but there was no consistent effect of cultivar in this tissue. The expression of the high sugar trait was generally positively correlated with transcript levels of fructosyltransferases. Presence and expression of only one of the two known 6G-FFT isoforms was positively correlated with high fructan biosynthesis, while the second isoform was associated with low fructan concentrations and positively correlated with fructan exohydrolase gene expression. The presence of distinct 6G-FFT sequence variants appears to be associated with the capacity of high sugar-content grasses to accumulate higher fructan levels particularly at warmer temperatures. These findings might be exploited for the selection and breeding of 'warm-effective' high sugar-content grasses to overcome some of the limitations of current high sugar-content ryegrass cultivars.