A majority of these loci were reviewed by Xia et al. They play different roles in flowering and maturity maintenance under diverse photoperiod patterns. To date, six of these loci, E1, E2, E3, E4, E9 and J, have been cloned. Among the six loci, E9 has been confirmed as GmFT2a, an orthologue of the Arabidopsis Flowering Locus T ( FT) gene, which plays an important role in flowering. įT, which encodes a putative florigen, is a key integrator gene in the regulation of flowering in Arabidopsis, and the function is highly conserved in different species. Ten FT-like genes have been identified in soybean among which GmFT2a and GmFT5a are confirmed as flowering promoters whereas GmFT1a is divergent as a floral and maturity inhibitor. GmFT2a and GmFT5a coordinately control flowering as flowering integrators and can be regulated by E1, E2, E3 and E4. Ectopic expression experiments in Arabidopsis also demonstrated that other soybean FT family genes including GmFT2b, GmFT3a, GmFT3b and GmFT5b promoted flowering, whereas GmFT4 delayed flowering. In transgenic soybean overexpressing E1, GmFT1a and GmFT4 expression was up regulated, whereas the expression of GmFT2a and GmFT5a was suppressed. Currently, a new GmFT2c was recently found inserted in a putative transponson in the third intron, and GmFT2d was determined structurally rearranged with some remnant in the genome, indicating that GmFT2 subclades ( GmFT2a, GmFT2b, GmFT2c and Gm FT2d) have different evolutionary trajectories. In plants, multiple regulation pathways regulate FT expression in response to diverse environmental signals, which enable flowering and other developmental responses to be seasonally timed. Different natural variations of FT promoter sequences are confirmed responsible for diverse flowering time in Arabidopsis and also in rice. The promoter of GmFT2a in soybean has high polymorphism, and some SNPs in the promoter region are associated with flowering time and photoperiod sensitivity. GmFT2a has a recessive allele for delayed flowering, which contains a Ty1/ copia-like retrotransposon SORE-1 inserted in the first intron that attenuates GmFT2a expression by its allele-specific transcriptional repression. Critical sequence polymorphism across the gene and its flanking regions may reflect the evolutionary process of species adapting to different environments.
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