Geminivirus-Mediated Delivery of Florigen to Ancestral Cotton Uncouples Flowering From Photoperiod and Promotes Determinate Growth

Ancestral cotton is a tropical perennial that flowers in response to short-day photoperiods whereas modern cultivars in the U.S. are day neutral and are grown as annuals.  Modern cultivars have restricted genetic diversity while primitive accessions are a tremendous reserve for desirable traits affecting fiber quality and biotic and abiotic stress tolerance.  However, differences in the onset of flowering complicate breeding between modern and ancestral lines and increase costs.  To induce early flowering in ancestral lines and facilitate breeding efforts, we have modified a disarmed Cotton Leaf Crumple Virus (CLCrV) [1] to express the Arabidopsis thaliana FLOWERING LOCUS T gene (FT, encoding florigen) from the coat-protein promoter, and used biolistic bombardment to infect the ancestral accession TX701.  Under long-day, greenhouse conditions, where TX701 would not normally flower, TX701 infected with pCLCrV::FT initiated reproductive growth concurrently with day-neutral cultivars.  Open flowers on induced TX701 plants were used as pollen donors to pollinate a day-neutral, modern cultivar, and F1 seeds were obtained.  The suitability of using “Virus-Induced Flowering” to facilitate breeding between short-day ancestral lines and modern cultivars is being further evaluated.  In addition to promoting flowering in long-day conditions, FT overexpression from the disarmed CLCrV backbone resulted in a more determinate (i.e., less vegetative) growth pattern that included shorter internodes and early termination of sympodial fruiting branches.  These findings will be discussed in relation to an emerging model that places FT and florigen in a signaling network that controls the indeterminate / determinate nature of meristems and primordia, such that it should be considered a general growth hormone rather than a flowering hormone.