Isolation and Gene Expression Analysis of Flowering-related Genes in Lettuce (Lactuca sativa L.)

Lettuce (Lactuca sativa L.) bolting is often limiting in agricultural production as stem elongation followed by flower bud differentiation results in unmarketable plants. Thus, to solve this problem, it is important to elucidate the molecular mechanisms controlling flowering. To investigate the relationship between gene expression and flowering in lettuce, homologs of flowering-related genes were isolated and their expression over time was analyzed in three cultivars and in one breeding line by using quantitative real-time PCR. In plants grown in the field, the expression of the lettuce homologues APETALA 1 (LsAP1L) and LEAFY (LsLFYL) in the shoot apex correlated with flower bud formation, and FLOWERING LOCUS T (LsFT) expression increased during the transition from vegetative to reproductive growth. The transcription of FLOWERING LOCUS D (LsFLDL), FVE (LsFVEL), and LUMINIDEPENDENS (LsLDL) also increased with flowering. Our previous study showed that LsFT was upregulated during lettuce flowering induced under controlled high temperature conditions. Results from both studies suggest that LsFT is involved in lettuce flowering, both in natural and controlled conditions. This is also the first report on the expression of other flowering-related genes along with flowering of lettuce grown in the field.