Functional and Genome Analysis of Cotton Growth Habit: Branching Architecture Is Regulated By the Gossypium hirsutum Single Flower Truss and Self-Pruning Orthologs

Domestication of upland cotton (Gossypium hirsutum) converted it from a lanky photoperiodic perennial to a day-neutral annual row-crop. Residual perennial traits, however, complicate crop management and more determinate architectures are desired. Cotton simultaneously maintains robust monopodial indeterminate shoots and sympodial determinate fruiting branches. We questioned if and how the FLOWERING LOCUS T (FT) / SINGLE FLOWER TRUSS (SFT)-like and TERMINAL FLOWER 1 (TFL1) / SELF-PRUNING (SP)-like genes control the balance of monopodial and sympodial growth in a woody perennial with complex growth habit. Virus-based manipulation of GhSP and GhSFT expression enabled unprecedented functional analysis of cotton development. GhSP maintains indeterminate growth in all apices; in its absence, both monopodial and sympodial branch systems precociously terminate as flowers, resulting in a remarkably determinate plant. GhSP is also essential to establish and maintain cambial activity; in its absence woody stems convert to a more herbaceous structure.  GhSFT encodes a florigenic signal stimulating rapid onset of sympodial branching and flowering in side shoots of wild photoperiodic and modern day-neutral accessions. High florigen levels did not alter monopodial apices, implying that once a cotton apex is SP-determined, it cannot be reset by florigen. Silencing GhSFT in day-neutral accessions delayed the onset of flowering, implying that deregulated florigen was a selection target during domestication. We show that members of the GhSFT and GhSP gene family, and associated gene networks, are ideal targets for further agricultural optimization. Supporting data from genome and transcriptome studies will be presented.