CRISPR/Cas9-mediated GhFT-targeted mutagenesis prolongs indeterminate growth and alters plant architecture in cotton

The shift from vegetative to reproductive growth is an important developmental transition that affects flowering and maturation, architecture, and ecological adaptability in plants. The florigen-antiflorigen system universally controls flowering and plant architecture, and changes to the ratio of these components alter this transition and disrupt growth. The genes FT (FLOWERING LOCUS T), encoding the florigen protein FT, and CETS [CENTRORADIALIS (CEN)/TERMINAL FLOWER1 (TFL1)/SELF-PRUNING (SP)], encoding antiflorigen proteins, have opposing roles. Upland cotton (Gossypium hirsutum) is one of the world's most widely cultivated cotton varieties, and its complex allotetraploid genome contains only one homoeologous pair of FT genes (GhFT-A and GhFT-D). The functionally conserved gene GhFT promotes flowering and plays a role in plant architecture, although the molecular regulation of flowering and plant architecture in cotton remains unclear. In this study, CRISPR/Cas9 technology was used to induce mutations in the first and second exons of GhFT, respectively. G. hirsutum cv. YZ-1 was transformed with a CRISPR/Cas9-GhFT vector using Agrobacterium tumefaciens, and a diverse set of mutations was identified at the editing site. Compared with the wild type, mutant plants could not transition between vegetative and reproductive growth, and significant alterations to plant architecture were observed. Quantitative RT-PCR revealed downregulation of the homologous floral meristem identity genes APETALA1 (GhAP1) and OVEREXPRESSION OF CONSTANS 1 (GhSOC1) and upregulation of the TFL1 homologs GhTFL1-1 and GhTFL1-2. These results suggested that GhFT played a significant role in flowering time and plant architecture and that the ratio of florigen-antiflorigen components was critical to producing improved cotton varieties. This study provided a basis for future investigations of molecular breeding in cotton and guidance for the agricultural production of this crop.