Genome-wide Analysis Of CPK Family And The Functional Identification Of CPKs Under Salt Stress In Upland Cotton

Soil salinization is one of the major environmental factor,which constraints to plant growth and agricultural production worldwide.Plants have developed important defensive responses that enable their survival and reproduction.Signaling components involving calcium(Ca²⁺)and the downstream calcium-dependent protein kinases?CPKs?play key roles in the perception and transduction of stress signals.In,?recent years,some CPKs have been reported to play important roles in plant response to salt stress.However,the study of CPKs in cotton and their functions in response to salt stress remain unexplored.The putative CPKs were determined by searching the cotton genome database of the allotetraploid upland cotton cultivar‘TM-1'with HMM?Hidden Markov Model?profiles constructed using CPK sequences from Arabidopsis,rice,maize,and grape as queries.All the putative CPKs were further subjected to Pfam and SMART analyses to identify their conserved domains and signature sequences.A total of 98 predicted CPKs were identified from upland cotton?Gossypium hirsutum L.‘TM-1'?,and phylogenetic analyses classified them into four groups.Gene family distribution studies have revealed the substantial impacts of the genome duplication events to the total number of GhCPKs.Transcriptome analyses showed a wide distribution of CPKs'expression among different organs.More than half were expressed at a low level across all 14 tissues,and about 25%of CPKs were observed to have a comprehensive expression range with consistently high expression in most tissues.A total of 19 CPKs were selected for their rapid responses to salt stress at the transcriptional level,most of which were also induced by the thylene-releasing chemical ethephon,suggesting a partal overlap of the salinity and ethylene responses.A total of 19 CPKs were selected for their rapid responses to salt stress at the transcriptional level,most of which were also induced by the thylene-releasing chemical ethephon,suggesting a partal overlap of the salinity and ethylene responses.Silencing of 4 of the 19 CPKs?GhCPK8,GhCPK38,GhCPK54,and GhCPK55?severely compromised the basal cotton resistance to salt stress.Our genome-wide expression analysis of CPK genes from up-land cotton suggests that CPKs are involved in multiple developmental responses as well as the response to different abiotic stresses.A cluster of the cotton CPKs was shown to participate in the early signaling events in cotton responses to salt stress.Our results provide significant insights on functional analysis of CPKs in cotton,especially in the context of cotton adaptions to salt stress.