Genome-wide identification of NAC gene family in pecan and its expression patterns during graft healing

The NAC gene family represents a class of plant-specific transcription factors characterized by a conserved NAC domain. These proteins exert pivotal regulatory influences in diverse biological processes, including plant growth and development, stress responses, and hormone signaling. Recent studies have further highlighted their core functions in graft union formation, scion-rootstock interactions, and the establishment of systemic functionality. In this study, we systematically identified the NAC gene family in pecan (Carya illinoinensis), revealing 116 CiNACs members distributed across.s 16 chromosomes. Phylogenetic analysis classified them into 16 subfamilies and 12 distinct groups, indicating evolutionary conservation of their functions. Interspecific collinearity analysis suggested that the family has undergone expansion and differentiation, leading to broad functional divergence. Furthermore, we screened six key CiNACs genes potentially associated with grafting and analyzed their expression patterns across different tissues, under drought stress, and during grafting via RNA-Seq and qRT-PCR. The results showed that, except for CiNAC24, the other five genes were significantly upregulated in stem tissues. Among them, the expression profiles of CiNAC24 and CiNAC72 implied a stronger responsiveness to abiotic stress rather than direct involvement in grafting. In contrast, CiNAC115 exhibited significant upregulation during grafting, suggesting its potential key role in regulating graft union formation. Collectively, this study provides important clues for elucidating the molecular mechanisms of CiNAC115 in grafting and lays a theoretical foundation for further uncovering the functions of the NAC gene family in the grafting process.