Identification of Tomato SET Domain Group Gene Family and Function Analysis Under Temperature Stress

Histone methylation plays important roles in plant development and adaptation to multiple stresses. SET domain group (SDG) proteins are identified as plant histone lysine methyltransferases in Arabidopsis and other crops. However, the SDG gene family and its functional roles in tomato remain unknown. In this research, 48 tomato SDG (SlSDG) gene family members were identified, and their chromosomal locations and conserved motifs were determined. According to phylogenetic analysis, the SlSDGs are divided into seven groups, which is consistent with Arabidopsis and rice. Promoter analysis indicated that the SlSDGs may be associated with biotic and abiotic stress responses. The expression pattern of SlSDGs illustrates that heat and cold stress significantly influence the transcript abundance of SDG14/19/21/23/48. The results of a VIGS assay showed that silencing SlSDG19 and SlSDG48 decreases tomato heat tolerance, while silencing SlSDG14 improves the heat tolerance of tomato plants. The analysis of downstream regulating genes indicated that heat shock proteins (HSPs), especially HSP70 and HSP90, act as critical effectors. Similarly, the experimental assay and expression analysis suggest that SDG21 and SDG23 positively and negatively regulate tomato cold tolerance through the CBF-COR pathway, respectively. These findings clarify the function of tomato SDG proteins and provide insight for the genetic improvement of tomato for temperature stress tolerance.