Genome-wide analysis of NAC transcription factors and exploration of candidate genes regulating selenium metabolism in Broussonetia papyrifera

Main conclusion Genome-wide identification revealed 79 BpNAC genes belonging to 16 subfamilies, and their gene structures and evolutionary relationships were characterized. Expression analysis highlighted their importance in plant selenium stress responses. Paper mulberry ( Broussonetia papyrifera ), a deciduous arboreal plant of the Moraceae family, is distinguished by its leaves, which are abundant in proteins, polysaccharides, and flavonoids, positioning it as a novel feedstock. NAC transcription factors, exclusive to plant species, are crucial in regulating growth, development, and response to biotic and abiotic stress. However, extensive characterization of the NAC family within paper mulberry is lacking. In this study, 79 BpNAC genes were identified from the paper mulberry genome, with an uneven distribution across 13 chromosomes. A comprehensive, genome-wide analysis of BpNACs was performed, including investigating gene structures, promoter regions, and chromosomal locations. Phylogenetic tree analysis, alongside comparisons with Arabidopsis thaliana NACs , allowed for categorizing these genes into 16 subfamilies in alignment with gene structure and motif conservation. Collinearity analysis suggested a significant homologous relationship between the NAC genes of paper mulberry and those in Morus notabilis , Ficus hispida , Antiaris toxicaria , and Cannabis sativa . Integrating transcriptome data and Se content revealed that 12 BpNAC genes were associated with selenium biosynthesis. Subsequent RT-qPCR analysis corroborated the correlation between BpNAC59 , BpNAC62 with sodium selenate, and BpNAC55 with sodium selenite. Subcellular localization experiments revealed the nuclear functions of BpNAC59 and BpNAC62 . This study highlights the potential BpNAC transcription factors involved in selenium metabolism, providing a foundation for strategically breeding selenium-fortified paper mulberry.