Changes in carbohydrate distribution in cotton photosynthetic organs and increase in boll weight reduce yield loss under high temperature.

Yield of cotton (Gossypium hirsutum) does not always fall with high temperature (HT) even though this induces significant reductions in fruit retention. To investigate the underlying mechanisms, a greenhouse experiment was conducted with two temperature regimes [control treatment, 28 °C; high temperature (HT), 34 °C] for 7 d. Results showed HT did not significantly influence cotton yield, but reduced boll number and increased boll weight. The 13C distribution ratio of the leaf subtending the cotton boll (LSCB) decreased while that of the cotton boll increased under HT. Transcriptomic and proteomic analyses of the LSCB revealed up-regulated genes involved in cytokinin and jasmonic acid synthesis, as well as SWEET15 (GH_D01G0218), which positively regulated photosynthesis and transport photosynthate, ultimately leading to increased boll weight. After 7 d recovery from HT, the 13C distribution ratio of the LSCB increased while that of the cotton boll decreased. However, boll weight still increased, which was related to increased amylase and sucrose phosphate synthase activities and up-regulated sucrose transport genes in the main-stem leaf and capsule wall. Thus, both accelerated sucrose synthesis and transport in the LSCB under HT and increased sucrose supply ability of the main-stem leaf and capsule wall after recovery from HT contributed to an increased boll weight, which finally maintained cotton yield.