Identification and characterization of cotton PHYTOCHROME-INTERACTING FACTORS in temperature-dependent flowering

PHYTOCHROME INTERACTING FACTORS (PIFs) integrate light and temperature signs to control plant growth and development. However, little is known about PIFs in crop plants such as cotton. Here, we identified 68 PIF proteins and their coding genes from an allotetraploid and three diploid ancestors. Cotton PIFs contain typical ACTIVEPHYA-BINDING (APA) and ACTIVE PHYB-BINDING (APB) motifs by which they bind to phytochrome phyA and phyB, respectively, and have a BASIC HELIX-LOOP-HELIX (bHLH) domain and a nuclear localization sequence necessary for bHLH-type transcription factors. Bioinformatics analysis showed that the promoter of each PIF gene contains multiple cis-acting elements and that the evolution of cotton genomes probably underwent loss, recombination, and tandem replication. Further observations indicated that the sensitivity of cotton PIF expression to high temperature was significantly different from that to low temperature. We found that allotetraploid Gossypium hirsutum PIF4a (GhPIF4a) was induced by high temperature. GhPIF4a promotes flowering in cotton and Arabidopsis and binds to the promoter of GhFT (G. hirsutum FLOWERING LOCUS T), and binding increased with increasing temperature. Our work identifies the evolutionary and structural characteristics and functions of PIF family members in cotton.