Genome-Wide Analysis of the Thioredoxin Gene Family in Gossypium hirsutum L. and the Role of the Atypical Thioredoxin Gene GhTRXL3-2 in Flowering

Thioredoxin (TRX) is a highly conserved low-molecular-weight protein and a ubiquitous antioxidant enzyme that plays key role in the regulation of plant growth and development. Here, using the whole-genome sequence, we performed a systematic analysis for the TRX gene family in upland cotton ( Gossypium hirsutum L.) and analyzed their structural characteristics, evolution, and expression profiles during growth and development. At least 86 GhTRX members, 40 typical and 46 atypical, were identified in the cotton genome, and they were unevenly distributed on the 26 chromosomes. Conserved domains and phylogenic tree construction classified the typical TRX gene family into seven subfamilies and the atypical TRX into nine subfamilies. An evolutionary analysis revealed that the TRX gene family underwent purification selection during evolution. In addition, an RNA-Seq analysis showed that, during vegetative and reproductive development, the differences in transcript abundance levels and organ-specific expression patterns suggest functional diversity. Biochemical assays demonstrated that the atypical TRX protein GhTRXL3-2 interacted with the cotton FLOWERING LOCUS T protein GhFT. The overexpression of GhTRXL3-2 in Arabidopsis thaliana resulted in early flowering compared with control plants. Additionally, the silencing of GhTRXL3-2 in cotton delayed maturation, suggesting that it has important roles in cotton’s flowering regulation. These results help clarify the evolution of the TRX genes and elucidate their biological functions in cotton flowering regulation.