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As one of the largest plant-specific gene families, the NAC transcription factor gene family plays important roles in various plant physiological processes that are related to plant development, hormone signaling, and biotic and abiotic stresses. However, systematic investigation of the NAC gene family in sea-island cotton (Gossypium babardense L.) has not been reported, to date. The recent release of the complete genome sequence of sea-island cotton allowed us to perform systematic analyses of G. babardense NAC GbNAC) genes. In this study, we performed a genome-wide survey and identified 270 GbNAC genes in the sea-island cotton genome. Genome mapping analysis showed that GbNAC genes were unevenly distributed on 26 chromosomes. Through phylogenetic analyses of GbNACs along with their Arabidopsis counterparts, these proteins were divided into 10 groups (I–X), and each contained a different number of GbNACs with a similar gene structure and conserved motifs. One hundred and fifty-four duplicated gene pairs were identified, and almost all of them exhibited strong purifying selection during evolution. In addition, various cis-acting regulatory elements in GbNAC genes were found to be related to major hormones, defense and stress responses. Notably, transcriptome data analyses unveiled the expression profiles of 62 GbNAC genes under Verticillium wilt (VW) stress. Furthermore, the expression profiles of 15 GbNAC genes tested by quantitative real-time PCR (qPCR) demonstrated that they were sensitive to methyl jasmonate (MeJA) and salicylic acid (SA) treatments and that they could be involved in pathogen-related hormone regulation. Taken together, the genome-wide identification and expression profiling pave new avenues for systematic functional analysis of GbNAC candidates, which may be useful for improving cotton defense against VW.

F-box proteins are substrate adaptors used by the SKP1–CUL1–F-box protein (SCF) complex, a type of E3 ubiquitin ligase complex in the ubiquitin proteasome system (UPS). SCF-mediated ubiquitylation regulates proteolysis of hundreds of cellular proteins involved in key signaling and disease systems. However, our knowledge of the evolution of the F-box gene family in Euarchontoglires is limited. In the present study, 559 F-box genes and nine related pseudogenes were identified in eight genomes. Lineage-specific gene gain and loss events occurred during the evolution of Euarchontoglires, resulting in varying F-box gene numbers ranging from 66 to 81 among the eight species. Both tandem duplication and retrotransposition were found to have contributed to the increase of F-box gene number, whereas mutation in the F-box domain was the main mechanism responsible for reduction in the number of F-box genes, resulting in a balance of expansion and contraction in the F-box gene family. Thus, the Euarchontoglire F-box gene family evolved under a birth-and-death model. Signatures of positive selection were detected in substrate-recognizing domains of multiple F-box proteins, and adaptive changes played a role in evolution of the Euarchontoglire F-box gene family. In addition, single nucleotide polymorphism (SNP) distributions were found to be highly non-random among different regions of F-box genes in 1092 human individuals, with domain regions having a significantly lower number of non-synonymous SNPs.

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