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.

As crucial enzymes in the lipid metabolic network, long-chain acyl-CoA synthases (LACSs) are members of the acyl-activated enzyme superfamily and play a crucial role in epidermal wax synthesis, plant lipid anabolic metabolism, and stress tolerance. In this study, 11 pecan LACS genes were identified and categorized into five groups and located on nine chromosomes. The significant degree of conservation in the AtLACS and CiLACS protein sequences was demonstrated by multiple sequence alignment and conserved motif analysis. Cis-acting element analysis identified numerous stress-responsive and hormone-inducible elements in the promoter regions of CiLACS genes. The expression levels of CiLACS9 and CiLACS9-1 were considerably up-regulated under salt and drought stress, according to the qRT-RCR study. Treatment with ABA also led to increased expression levels of CiLACS1, CiLACS1-1, CiLACS2, and CiLACS9-1. Notably, CiLACS4, CiLACS4-1, CiLACS9, and CiLACS9-1 exhibited peak expression levels at 135 days after anthesis and are likely to have been crucial in the accumulation of seed kernel oil. Moreover, the CiLACS9 gene was shown to be located in the cytoplasm. These findings offer a theoretical framework for clarifying the roles of LACS genes in the processes of pecan kernel oil synthesis and response to abiotic stressors.

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.

Pecan seed oil is a valuable source of essential fatty acids and various bioactive compounds; however, the functions of microRNAs and their targets in oil biosynthesis during seed development are still unknown. Here, we found that the oil content increased rapidly in the three early stages in three cultivars, and that oleic acid was the predominant fatty acid component in the mature pecan embryos. We identified, analyzed, and validated the expression levels of miRNAs related to seed development and oil biosynthesis, as well as their potential target genes, using small RNA sequencing data from three stages (120, 135, and 150 days after flowering). During the seed development process, 365 known and 321 novel miRNAs were discovered. In total, 91 known and 181 novel miRNAs were found to be differentially expressed, and 633 target genes were further investigated. The expression trend analysis revealed that the 91 known miRNAs were classified into eight groups, approximately two-thirds of which were up-regulated, whereas most novel miRNAs were down-regulated. The qRT–PCR and degradome sequencing data were used to identify five miRNA- target pairs. Overall, our study provides valuable insights into the molecular regulation of oil biosynthesis in pecan seeds.

Mitogen-activated protein kinases consist of three kinase modules composed of MPKs, MKKs, and MPKKKs. As members of the protein kinase (PK) superfamily, they are involved in various processes, such as developmental programs, cell division, hormonal progression, and signaling responses to biotic and abiotic stresses. In this study, a total of 18 MPKs and 10 MKKs were annotated on the pecan genome, all of which could be classified into four subgroups, respectively. The gene structures and conserved sequences of family members in the same branch were relatively similar. All MPK proteins had a conserved motif TxY, and D(L/I/V)K and VGTxxYMSPER existed in all MKK proteins. Duplication events contributed largely to the expansion of the pecan MPK and MKK gene families. Phylogenetic analysis of protein sequences from six plants indicated that species evolution occurred in pecan. Organ-specific expression profiles of MPK and MKK showed functional diversity. Ka/Ks values indicated that all genes with duplicated events underwent strong negative selection. Seven CiPawMPK and four CiPawMKK genes with high expression levels were screened by transcriptomic data from different organs, and these candidates were validated by qRT-PCR analysis of hormone-treated and stressed samples.

Nitrogen (N) is an important mineral nutrient for plant growth, as well as a limiting factor for crop yield, and how to improve the utilization efficiency of N fertilizer by plants is currently a research hotspot. This article uses bioinformatics methods to identify and analyze members of the glutamine synthetase (GS) and glutamate synthase (GOGAT) gene families in pecan. A total of 6 GS genes and 4 GOGAT genes were identified, and their physicochemical properties, gene structures, and homologous evolutionary relationships were analyzed. Analysis of tissue-specific expression of GS and GOGAT genes based on transcriptome data from pecan. The enzyme activities of GS and GOGAT and the gene expression were quantitatively analyzed under different N form ratios in pecan. According to the results, the promoter cis-acting elements of GS and GOGAT genes can be roughly divided into three types: light-responsive elements, hormone-responsive elements, and stress-responsive elements. The results of homologous evolution showed that there was no tandem duplication event for the two gene families, and GS and GOGAT have undergone purification during the evolutionary process. CiGS2s and CiFd-GOGATs were expressed mainly in leaves, and CiNADH-GOGATs were expressed mainly in fruits. The qPCR analysis results showed that T4 treatment significantly increased the expression levels of CiGS and CiGOGAT genes in the leaves. The enzyme activities of GS and GOGAT in pecan were significantly increased under T3, T4, and T5 treatments. In summary, a higher proportion of ammonium nitrogen (NH4+) in the nutrient solution was profit to pecan NH4+ assimilation. This study determined the appropriate nitrogen ratio for pecan, promoting a theoretical basis for reducing environmental pollution caused by nitrogen fertilizer and improving the nitrogen utilization efficiency of pecan. In summary, both CiGSs and CiGOGATs exhibit tissue specificity, and an ammonium-nitrate mixture with a higher proportion of NH4+ is more favorable for NH4+ assimilation in pecan. This study provides a reference basis for further understanding the functions of CiGSs and CiGOGATs in pecan, and offers a theoretical foundation for improving N use efficiency in pecan.