Genome-wide identification of isopentenyl transferase genes in cotton and their roles in regulating vegetative branching after topping

The promotion of vegetative branching in plants after topping has been observed without a clear understanding of the underlying mechanism. This study aimed to investigate the role of isopentenyl transferase (IPT) and cytokinins in the regulation of vegetative branching in cotton (Gossypium hirsutum L.), hypothesizing that they play key roles in this process. Plant topping was implemented at peak flowering stage in field-grown cotton, and seedcotton yield, yield components, vegetative branching, fruiting, and cytokinin levels were examined over two consecutive years. The results showed that plant topping significantly enhanced the growth and development of vegetative branches, as evidenced by increased biomass, leaf area, and fruiting of vegetative branches, along with an accumulation of cytokinin accumulation at the tips of vegetative branches. This led to a 10.3 % rise in boll density and an 11.4 % increase in seedcotton yield compared with the non-topped control. The analysis of RNA-seq and qRT-PCR data revealed significant differences in the expression patterns of IPT genes, suggesting their importance in regulating the growth and development of vegetative branches. Furthermore, examing the IPT gene families in diploid and tetraploid cotton species identified a total of 8, 8, 16, and 16 IPT genes, categorized into 6 groups. Prediction of cis-acting elements of GhIPT gene family promoters and analysis of their expression profiles demonstrated the involvement of GhIPT genes in multiple plant growth pathways with specific spatio-temporal expression. The findings underline that plant topping enhances cytokinins accumulation at vegetative branch tips by up-regulating IPT genes, leading to increased vegetative branching, fruiting, and ultimately, seedcotton yield. This study provides valuable insights into enhancing cotton yield formation through the regulation of growth and development of vegetative branches by GhIPTs and offers a crucial reference for further investigations into the functions of IPT genes.