Genomic Identification of Callose Synthase (CalS) Gene Family in Sorghum (Sorghum bicolor) and Comparative In Silico Expression Analysis under Aphid (Melanaphis sacchari) Infestation

Callose is widely present in higher plants and plays a significant role in plant growth, development, and response to various stresses. Although numerous studies have highlighted the importance of the callose synthase (CalS) genes, their role in the resistance of sorghum (Sorghum bicolor) to aphids (Melanaphis sacchari) remains limitedly understood. This study identified 11 sorghum callose synthase genes (SbCalS), unevenly distributed across four chromosomes of sorghum. All SbCalS proteins contain glucan synthase and Fks1 domains, with segmental duplication playing a major role in gene diversification. Cis-element prediction revealed the presence of numerous stress-responsive elements, indicating that this gene family is primarily involved in stress resistance. Using published RNA-seq data, we discovered the differential expression of the SbCalS5 gene between resistant and susceptible sorghum varieties. Real-time quantitative PCR (qPCR) analysis confirmed the relative expression levels of all SbCalS members under aphid stress. To further verify the role of callose in sorghum, we measured the callose content in both resistant and susceptible sorghum varieties. The results indicated that callose plays a critical role in aphid resistance in sorghum, particularly the SbCalS5 gene. This study provides a reference for further investigation into the role of callose synthase genes in sorghum aphid resistance.