Identification of biological rhythms related GIGANTEA genes in tomato and functional analysis under heat stress

GIGANTEA (GI) is a protein that regulates circadian rhythms and is essential for various physiological processes that influence abiotic stress resistance in plants. However, when tomatoes were exposed to high temperatures, their biological rhythms were disrupted. We identified and characterized two GI genes in the complete tomato genome, located on chromosomes 4 (SlGI.04) and 12 (SlGI.12), and examined the protein characteristics, gene structure, phylogenetic relationships, and homology. Promoters of SlGI.04 and SlGI.12 contained many cis-regulatory elements associated with growth, hormone responses, and abiotic stress, and the expression patterns of SlGIs exhibited circadian rhythms, responded to heat stress, and showed organ specificity. Subcellular localization confirmed that SlGI.04 and SlGI.12 resided in the nucleus, and analysis of potential interacting proteins indicated their involvement in stress responses and developmental processes. Silencing SlGI.04 and SlGI.12 impaired heat stress resistance in tomato, leading to severe damage in silenced seedlings. Under heat stress, silenced plants were more sensitive to heat stress treatment than pTRV2 plants. pTRV2-SlGI.04 and pTRV2SlGI.12 plants exhibited significantly reduced levels of soluble sugars, soluble proteins, and proline, impaired antioxidant ability, and significant down-regulation of heat stress-related gene expression compared with those of pTRV2 plants. These results indicated that GI genes play an active role in tomato responses to abiotic stress and that SlGIs might mediate responses to high-temperature stress by regulating genes associated with antioxidant enzymes or heat-related processes in tomato. These findings provide a foundation for further research into its functional role and potential molecular mechanisms of heat tolerance in tomato.