Promoter variation and transcript divergence in Brassicaceae lineages of FLOWERING LOCUS T.
Brassica napus (AACC, 2n = 38), an oil crop of world-wide importance, originated from interspecific hybridization of B. rapa (AA, 2n = 20) and B. oleracea (CC, 2n = 18), and has six FLOWERING LOCUS T (FT) paralogues. Two located on the homeologous chromosomes A2 and C2 arose from a lineage distinct from four located on A7 and C6. A set of three conserved blocks A, B and C, which were found to be essential for FT activation by CONSTANS (CO) in Arabidopsis, was identified within the FT upstream region in B. napus and its progenitor diploids. However, on chromosome C2, insertion of a DNA transposable element (TE) and a retro-element in FT upstream blocks A and B contributed to significant structural divergence between the A and C genome orthologues. Phylogenetic analysis of upstream block A indicated the conserved evolutionary relationships of distinct FT genes within Brassicaceae. We conclude that the ancient At-α whole genome duplication contributed to distinct ancestral lineages for this key adaptive gene, which co-exist within the same genus. FT-A2 was found to be transcribed in all leaf samples from different developmental stages in both B. rapa and B. napus, whereas FT-C2 was not transcribed in either B. napus or B. oleracea. Silencing of FT-C2 appeared to result from TE insertion and consequent high levels of cytosine methylation in TE sequences within upstream block A. Interestingly, FT-A7/C6 paralogues were specifically silenced in winter type B. napus but abundantly expressed in spring type cultivars under vernalization-free conditions. Motif prediction indicated the presence of two CO protein binding sites within all Brassica block A and additional sites for FT activation in block C. We propose that the ancestral whole genome duplications have contributed to more complex mechanisms of floral regulation and niche adaptation in Brassica compared to Arabidopsis.
National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, People's Republic of China.
Jing
J
Wang
Clare J
CJ
Hopkins
Jinna
J
Hou
Xiaoxiao
X
Zou
Chongnan
C
Wang
Yan
Y
Long
Smita
S
Kurup
Graham J
GJ
King
Jinling
J
Meng
D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D029688:Brassica napus / Q000235:genetics; D019607:Brassicaceae / Q000235:genetics*; D032461:Chromosomes, Plant; D017124:Conserved Sequence; D019175:DNA Methylation; D004171:Diploidy; D019143:Evolution, Molecular; D035264:Flowers / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D014644:Genetic Variation; D018745:Genome, Plant; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D057891:Tetraploidy
D010940:Plant Proteins