Genome-Wide Characterization of the ANN Gene Family in <em>Corydalis saxicola</em> and the Role of CsANN1 in Dehydrocavidine Biosynthesis

Annexins (ANNs), which are calcium (Ca2+)-dependent and phospholipid-binding protein families, are implicated in the regulation of plant growth and development as well as protection from various stresses. However, little is known about ANNs in Corydalis Saxicola, an endangered benzylisoquinoline alkaloid (BIA)-riched herbaceous plant widely used in traditional Chinese medicine and endemic to the calciphilic karst region in China. Here, nine CsANN genes were identified from C. saxicola, and they were divided into three subfamilies based on the phylogenetic analysis. The CsANNs clustered into the same clade, sharing similar gene structures and conserved motifs. The nine CsANN genes were located on five chromosomes, and their expansions were mainly attributed to tandem duplication and segmental duplication. The CsANN transcripts showed variable organ-specific and Ca2+-responsive expression patterns. Further transient overexpression assays showed that CsANN1 could positively regulate the accumulation of BIA compounds in C. saxicola leaves, probably through directly interacting with key BIA-biosynthesis-pathway enzymes or by interacting with BIA-biosynthesis-regulating factors, such as MYBs. This study sheds light on profiles and functions of the CsANN gene family and paves the way for unraveling the molecular mechanism of BIA accumulation regulated by Ca2+ through CsANNs.