EMBRYONIC FLOWER2B, coming from a stable QTL, represses the floral transition in cotton

The EMBRYONIC FLOWER 2 (EMF2) gene encodes a VEFS (VRN2-EMF2-FIS2-Su(z)12) domain protein involved in plant growth and development. Herein, genome-wide characterization of the VEFS-box gene family in Gossypium raimondii, G. arboreum, G. barbadense, and G. hirsutum was performed with a total of 3, 3, 6, and 6 homologous sequences respectively identified in the four species. The gene structure, protein motifs, and gene expression were further investigated. Based on our previous research on multiple stable quantitative trait loci for early maturity, GhEMF2B on chromosome D03 was selected as a candidate gene for further study. Quantitative real-time PCR analysis indicated that GhEMF2B was upregulated in the apical buds of late-maturing cultivars at the fourth and fifth true-leaf stages compared to that of early-maturing cultivars. Virus-induced gene silencing of GhEMF2B in cotton seedlings repressed expression by 50%-70%, which led to earlier floral bud development, young curled leaves, and abnormal petal formation. Further analysis demonstrated that the silencing of GhEMF2B enhanced the expression levels of the positive floral regulators AGAMOUS-LIKE 6 (GhAGL6), FLOWERING LOCUS T (GhFT), and APETALA 1 (GhAP1). Thus, it can be inferred that GhEMF2B plays important roles in the floral transition and development of cotton.