Genome-wide identification of the histone acetyltransferase gene family in Citrus clementina and its potential roles in citrate metabolism

Histone acetyltransferase (HAT) catalyzes histone acetylation and is involved in plant growth and development and stress responses. Here, 37 CitHAT genes were identified in Citrus clementina. Their physicochemical properties, chromosomal location, gene structure, conserved domain and motif, and cis-acting elements were characterized. CitHATs were classified into four subfamilies based on protein sequence homology, which was strongly supported by gene structure, conserved domain, and motif analysis. The cis-acting elements in gene promoter regions were predicted to be associated with the regulation of plant growth, stress resistance, and response to hormones. Phenotypic and transcriptomic analyses of citrus callus with mock treatment and HAT inhibitor treatment revealed that increased citric acid content in inhibitor treatment may be attributed to differential expression of CitPEPCK2 and CitGS2, which may be due to the hypo-acetylation of histone H3. The expression patterns of CitHATs in citrus fruit development stages showed that CitHAG11 and CitHAG28 exhibited a negative correlation with citric acid content. Our study associates the potential function of histone acetyltransferases in citrate metabolism and extends the molecular mechanism of citrate metabolism in fruits.