Analyses of open-access multi-omics data sets reveal genetic and expression characteristics of maize ZmCCT family genes

Flowering in maize (Zea mays) is influenced by photoperiod. The CO, CO-like/COL and TOC1 (CCT) domain protein-encoding genes in maize, ZmCCTs, are particularly important for photoperiod sensitivity. However, little is known about CCT protein-encoding gene number across plant species or among maize inbred lines. Therefore, we analysed CCT protein-encoding gene number across plant species, and characterized ZmCCTs in different inbred lines, including structural variations (SVs), copy number variations (CNVs), expression under stresses, dark-dark (DD) and dark-light (DL) cycles, interaction network and associations with maize quantitative trait loci (QTLs) by referring to the latest v4 genome data of B73. Gene number varied greatly across plant species, more in polyploids than in diploids. The numbers of ZmCCTs identified were 58 in B73, 59 in W22, 48 in Mo17, and 57 in Huangzao4 for temperate maize inbred lines, and 68 in tropical maize inbred line SK. Some ZmCCTs underwent duplications and presented chromosome collinearity. Structural variations and CNVs were found but they had no germplasm specificity. Forty-two ZmCCTs responded to stresses. Expression of 37 ZmCCTs in embryonic leaves during seed germination of maize under DD and DL cycles was roughly divided into five patterns of uphill pattern, downhill-pattern, zigzag-pattern, └-pattern and ⅃-pattern, indicating some of them have a potential to perceive dark and/or dark-light transition. Thirty-three ZmCCTs were co-expressed with 218 other maize genes; and 24 ZmCCTs were associated with known QTLs. The data presented in this study will help inform further functions of ZmCCTs.