GENETIC CONTROL OF FLOWERING IN PERENNIAL RYEGRASS

¹ DLF-Trifolium Ltd., 31 Hoejerupvej, Box 19, DK-4660 Store Heddinge, Denmark

² Risoe National Laboratory, Plant Research Department, Box 49, DK-4000 Roskilde, Denmark

DLF-TRIFOLIUM is a major European seed company with a long history in grass improvement by traditional breeding methods. Within the last decade, plant biotechnology and molecular marker technologies have been developed and increasingly employed in R&D activities. A major research focus area has been the genetic control of flowering in perennial ryegrass, Lolium perenne and major progress has been made towards technologies for the repression of flowering. Based on sequence homology and differential screenings, a range of genes has been isolated showing homology to genes controlling the floral transition in Arabidopsis thaliana and other plant species. Key regulatory genes have been identified and selected members have been tested for effects on flowering characteristics in grasses and Arabidopsis. Expression of the Lolium perenne homologue of Terminal Flower1, LpTFL1, was found to complement the Arabidopsis tfl1-14 mutant and constitutive expression of LpTFL1 was found to repress flowering in both red fescue and perennial ryegrass with a good correlation between the flowering repression phenotype and the level of LpTFL1 expression. Conserved function of the Lolium perenne CONSTANS gene, LpCO, has likewise been demonstrated by complementation studies in the co-2 Arabidopsis mutant background. Interestingly, the LpCO lacks the second zink-finger B-box found in the Arabidopsis CO. Differential Display screening resulted in a collection of differentially regulated MADS-box genes of which some are up-regulated very early during vernalization and are likely to represent floral enhancers. Others were found to be down-regulated equally early during vernalization and are likely to represent floral inhibitors.