Genome-Wide Analysis of Callose Synthase (CALS) Genes in Cabbage (Brassica oleracea var. capitata L.): Identification and Expression Profiling During Hyaloperonospora parasitica Infection

Callose synthase (<i>CALS</i>) genes are known to play critical roles in microspore development and in plant responses to diverse biotic and abiotic stresses. While the role of <i>CALS</i> genes has been extensively characterized in several plant species, their homologs in <i>Brassica oleracea</i> (<i>BoCALS</i>) remain understudied. In this study, 15 <i>BoCALS</i> genes were identified in <i>B. oleracea</i> genome, distributed across eight chromosomes. All BoCALS proteins contain Glucan-synthase and Fks1 domains. Phylogenetic analysis grouped <i>BoCALS</i> and their homologs from <i>Arabidopsis thaliana</i> and <i>Brassica rapa</i> into three distinct Clusters (Ⅰ-Ⅲ), revealing conserved evolutionary relationships within the <i>Brassicaceae</i> family. Collinearity analysis showed that <i>AtCALS</i> genes of <i>Arabidopsis</i> have multiple orthologs in <i>B. oleracea</i>. Analysis of RNA-Seq data from public databases suggested that most of the <i>BoCALS</i> genes exhibit tissue-specific expression patterns, indicating their potential roles in organ differentiation and development. QRT-PCR analysis elucidated a different expression level of <i>BoCALS</i> genes in response to <i>Hyaloperonospora parasitica</i> infection. Notably, <i>BoCALS6</i> expression was significantly higher in resistant varieties compared to susceptible varieties and further up-regulated following <i>H. parasitica</i> infection, indicating its potential role in downy mildew resistance. This study presents the first comprehensive characterization of <i>BoCALS</i> gene family in <i>B. oleracea</i> and provides a foundation for further functional investigations into their roles in downy mildew resistance.