Isolation, identification and expression patterns of RoLEAFY in non-recurrent and recurrent flowering roses

摘要

Recurrent flowering is an important characteristic in modern roses. Previous studies indicate that RoTFL1 (RTFL1c, RoKSN) plays an important role in this trait, but homologues of its downstream target gene LEAFY (LFY) have not been identified in roses. In this study, we isolated LFY homologues from three Rosa species (here collectively designated Rosa LEAFY [RoLFY]) with recurrent or non-recurrent flowering habits. The RoLFY genes were isolated from Rosa chinensis, R. multiflora, and R. rugosa using a combination of degenerate and gene-specific primers by thermal asymmetric interlaced-PCR and normal PCR. The full-length cDNA was 2142 bp. The coding sequence was 1242 bp and encoded 413 amino acids. The sequence identity among the three species was 96.1%, compared with 572% with Arabidopsis LFY. A phylogenetic analysis clustered the RoLFY proteins in one group, which was most similar to LFY homologues of strawberry (FaLFY) within the Rosaceae. The deduced tertiary structure of the RoLFY proteins was almost identical and the domains were consistent with those of FaLFY-2 from strawberry. The RoLFY protein was localized in the nucleus consistent with other transcription factors. Over-expression of RoLFY promoted reproductive growth and earlier flowering in transgenic Arabidopsis. Marked differences in expression levels were detected during early flower bud development, but not at subsequent stages, among the non-recurrent flowering R. multiflora and R. rugosa, and the recurrent flowering R. chinensis. These results suggest that once floral initiation is complete, recurrent-flowering roses can flower continuously without repeated accumulation of RoLFY mRNA.