Genome-wide identification of ABCC gene family and their expression analysis in pigment deposition of fiber in brown cotton (Gossypium hirsutum)

ABC (ATP-binding cassette) transporters are a class of superfamily transmembrane proteins that are commonly observed in natural organisms. The ABCC (ATP-binding cassette C subfamily) protein belongs to a subfamily of the ABC protein family and is a multidrug resistance-associated transporter that localizes to the tonoplast and plays a significant role in pathogenic microbial responses, heavy metal regulation, secondary metabolite transport, and plant growth. Recent studies have shown that the ABCC protein is also involved in the transport of anthocyanins/proanthocyanidins (PAs). To clarify the types and numbers of ABCC genes involved in PA transport in Gossypium hirsutum, the phylogenetic evolution, physical location, and structure of ABCC genes were classified by bioinformatic methods in the upland cotton genome, and the expression levels of these genes were analyzed at different developmental stages of the cotton fiber. The results showed that 42 ABCC genes were initially identified in the whole genome of upland cotton; they were designated GhABCC1-42. The gene structure and phylogenetic analysis showed that the closely related ABCC genes were structurally identical. The analysis of chromosomal localization demonstrated that there were no ABCC genes on the chromosomes of AD/At2, AD/At5, AD/At6, AD/At10, AD/At12, AD/At13, AD/Dt2, AD/Dt6, AD/Dt10, and AD/Dt13. Outside the genes, there were ABCC genes on other chromosomes, and gene clusters appeared on the two chromosomes AD/At11 and AD/Dt8. Phylogenetic tree analysis showed that some ABCC proteins in G. hirsutum were clustered with those of Arabidopsis thaliana, Vitis vinifera and Zea mays, which are known to function in anthocyanin/PA transport. The protein structure prediction indicated that the GhABCC protein structure is similar to the AtABCC protein in A. thaliana, and most of these proteins have a transmembrane domain. At the same time, a quantitative RT-PCR analysis of 42 ABCC genes at different developmental stages of brown cotton fiber showed that the relative expression levels of GhABCC24, GhABCC27, GhABCC28, GhABCC29 and GhABCC33 were consistent with the trend of PA accumulation, which may play a role in PA transport. These results provide a theoretical basis for further analysis of the function of the cotton ABCC genes and their role in the transport of PA.