Evolution Of The CPK Gene Family In Hemiboea Subcapitata And Green Plants

CPK（Calcium-dependent protein kinase）gene family,which can be activated directly by Ca²⁺,are widely present in green plants and play an important role in Ca²⁺signal transduction and stress response.The habitats in karst areas are fragile and the soil Ca²⁺content is high.So far,there are few researches on CPK gene evolution for endemic species in karst area.In this study,Hemiboea subcapitata（Gesneriaceae）,widely distributed in karst area,was used to conduct this issue.The CPK gene was identified from the whole genome data of H.subcapitata,and the methods of phylogenetic,conserved motif and gene structure,collinearity,selection pressure and expression were used to detect the evolution of CPK gene family.In addition,the CPK gene were identified through green plants,including algae,bryophytes,lycopus,ferns,gymnosperms,and angiosperms.The methods of phylogenetic,conserved motifs structure,copy number variation were employed to reconstruct the evolutionary framework of CPK gene family in green plants.These results would be significant to more comprehensively explore the evolutionary history of CPK gene family in green plants.The main results are as follows:（1）The CPK gene family is highly conserved in H.subcapitata,and the fragment replication is attributed to the expansion of this gene family.32 CPK genes were identified in H.subcapitata.Among 32 CPK genes are identified in H.subcapitata,10 gene pairs of which are generated by fragment replication.The CPK gene family divide into four subgroups,subgroupⅠand Ⅱ contains 11 members and 8members respectively,and they forms a clade;subgroupⅢcontains 11 members;subgroupⅣonly includes 2 members,and it is the basal clade.The motif structure of CPK gene family in H.subcapitata is highly similar.The number of introns in subgroupⅠcontains 7 members,subgroupⅡcontains 8 members,subgroupⅢcontains 7-8 members,subgroupⅣcontains 12 members.This gene family experienced intron loss during evolution.SubgroupsⅠandⅡwere strongly positively selected,while subgroupsⅢandⅣwere neutrally selected.Members of subgroupsⅠandⅡmay be retained due to environmental adaptation,which may be related to the adaptation of H.subcapitata to the habitat in karst area.The CPK gene family has expressed in different organs（root,leaf,and flower）and different developmental stages of H.subcapitata.（2）CPK gene family gradually have expanded with the evolution of green plants.The most recent common ancestor of green algae and land plants has at least one CPK gene;CPK gene experienced multiple gene acquisition and loss events during the evolution of green plants.The CPK gene family began to expand in bryophytes,and continued to expand in lycopus,ferns and angiosperms,while it contracted in gymnosperms.In green algae,CPK genes formed a unique evolutionary clade and contains a few genes.CPK genes of land plants can be divided into four subgroups:the phylogenetic relationship between subgroupⅠandⅡis closer;the gene members of subgroupⅣdiverged first.Large-scale replication events may lead to the expansion of CPK gene family.The significant expansion of CPK gene family in land plants would be related to the adaptation of the diverse environment of land ecosystems.Generally,the CPK gene family is an ancient and highly conserved gene family.The expansion and evolution of this gene family in the karst-suitable species H.subcapitata may be related to its adaptation to calcium-rich and stressed habitats in karst area.The CPK gene family has a complex evolutionary history in green plants,with significant expansions in Physcomitrella patens and angiosperms.We hypothesize that the CPK gene family plays an important role in major evolutionary events such as plant adaptation to land and angiosperms diversification.