Background Calcium (Ca2+) serves as a ubiquitous second messenger and plays a pivotal role in signal transduction. Calcineurin B-like proteins (CBLs) are plant-specific Ca2+ sensors that interact with CBL-interacting protein kinases (CIPKs) to transmit Ca2+ signals. CBL-CIPK complexes have been reported to play pivotal roles in plant development and response to drought stress; however, limited information is available about the CBL and CIPK genes in pecan, an important nut crop. Results In the present study, a total of 9 CBL and 30 CIPK genes were identified from the pecan genome and divided into four and five clades based on phylogeny, respectively. Gene structure and distribution of conserved sequence motif analysis suggested that family members in the same clade commonly exhibited similar exon-intron structures and motif compositions. The segmental duplication events contributed largely to the expansion of pecan CBL and CIPK gene families, and Ka/Ks values revealed that all of them experienced strong negative selection. Phylogenetic analysis of CIPK proteins from 14 plant species revealed that CIPKs in the intron-poor clade originated in seed plants. Tissue-specific expression profiles of CiCBLs and CiCIPKs were analysed, presenting functional diversity. Expression profiles derived from RNA-Seq revealed distinct expression patterns of CiCBLs and CiCIPKs under drought treatment in pecan. Moreover, coexpression network analysis helped to elucidate the relationships between these genes and identify potential candidates for the regulation of drought response, which were verified by qRT–PCR analysis. Conclusions The characterization and analysis of CBL and CIPK genes in pecan genome could provide a basis for further functional analysis of CiCBLs and CiCIPKs in the drought stress response of pecan.

Plant R2R3-MYBs comprise one of the largest transcription factor families; however, few R2R3-MYB genes in pecan have been functionally analyzed due to the limited genome information and potential functional redundancy caused by gene duplication. In this study, 153 R2R3-MYB genes were identified and subjected to comparative phylogenetic analysis with four other plant species. Then, the pecan R2R3-MYB gene family was divided into different clades, which were also supported by gene structure and motif composition results. Fifty-two duplication events including 77 R2R3-MYB genes were identified in this gene family, and Ka/Ks values showed that all of the duplication events were under the influence of negative selection. Expression levels of pecan R2R3-MYB genes during the graft union formation process were further investigated using RNA-seq with four different timepoints after grafting, namely, 0, 8, 15 and 30 d. Sixty-four differentially expressed R2R3-MYB genes were identified and showed different expression patterns after grafting. Co-expression networks were further constructed to discover the relationships between these genes. The co-expression networks contained 57 nodes (R2R3-MYB genes) and 219 edges (co-expression gene pairs) and CIL1528S0032 contained the maximum number of edges. Fifteen genes contained more than 10 edges; the majority of these were up-regulated during graft union formation and verified by qRT-PCR. This study provides a foundation for functional analysis to investigate the roles that R2R3-MYBs play in graft union formation in pecan and identify the key candidate genes.

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Pecan (Carya illinoinensis) is an economically important nut tree that is greatly affected by drought, limiting its production and distribution. Although the complete genome of the pecan was published several years ago, the molecular basis of the pecan’s response to drought remains unclear. In this study, we analyzed the high-throughput transcriptome data for pecans under 3, 6, 9, 12, and 15 days of drought stress compared with the controls. A total of 12,893 differentially expressed genes (DEGs) were identified under drought stress, with 11,684 of them showing significant changes after 15 d of drought treatment. Among these, 4448 genes were up-regulated while 7226 were down-regulated. The trend analysis revealed that DEGs could be classified into 20 clusters. Surprisingly, the majority of genes (6148) showed a gradual down-regulation, and 3683 genes showed a gradual up-regulation in response to drought. Gene ontology enrichment analysis showed that the DEGs were mainly enriched in biological processes. The KEGG pathway enrichment results indicated that the DEGs were mainly enriched in several pathways, including metabolic pathways, the biosynthesis of secondary metabolites, and plant hormone signal transduction processes. Among the DEGs, 457 protein kinase and 734 transcription factor genes were shown to be drought-responsive and may play key roles in the response to drought, and the expression patterns of selected candidate genes were further validated using quantitative real-time PCR. Collectively, these findings highlighted the multiple processes in pecans under drought stress and provided valuable insights into the further investigation of the functions of drought stress-responsive genes and the molecular basis of the pecan drought stress response.

Aux/IAA (Auxin/Indole-3-Acetic Acid) family, one of the early response gene family of auxin signals, is involved in regulating numerous aspects of plant growth and development. As an important economic plant, the identification of Aux/IAA family genes in pecan is of great significance. In this study, a total of 37 Aux/IAA family genes were identified in the pecan genome using bioinformatics method, subcellular localization revealed that all its members are located in the nucleus. Based on the phylogenic relationship with Arabidopsis Aux/IAAs gene, the 37 pecan Aux/IAA gene were categorized into two major groups (A and B). Multiple sequence alignment analysis showed that there were four typical conserved domains (I-IV) in Aux/IAA proteins of pecan. The cis-acting elements analysis revealed that all pecan Aux/IAAs had cis-acting elements in response to hormones in the promoter regions. According to the expression patterns of pecan Aux/IAA genes during graft healing, four genes with high expression were identified, which may play important roles in the formation of graft union in pecan. This study will be helpful to elucidate the function of pecan Aux/IAAs in the process of graft healing and find candidate genes.