Ascorbate oxidase (AAO) plays an important role in maintaining cellular redox homeostasis, thereby influencing plant growth, development, and responses to both biotic and abiotic stresses. However, there has been no systematic characterization of
AAO genes in
Citrus, especially their roles in response
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Ascorbate oxidase (AAO) plays an important role in maintaining cellular redox homeostasis, thereby influencing plant growth, development, and responses to both biotic and abiotic stresses. However, there has been no systematic characterization of
AAO genes in
Citrus, especially their roles in response to cold stress. In the present study, nine
AAO genes were identified in
C. sinensis through bioinformatics analyses, exhibiting uneven distribution across four chromosomes. All CsAAOs possessed three conserved domains and were predicted to localize in the apoplast. The
CsAAO gene family displayed varied intron–exon patterns. Phylogenetic analysis categorized the
CsAAO family into three main clades (Clade A–C), suggesting distinct biological functions. Collinearity and Ka/Ks analysis revealed three duplicate gene pairs within the
CsAAO gene family, with all duplicated CsAAOs primarily evolving under purifying selection. Analysis of
cis-acting elements showed the presence of multiple hormone response elements and stress response elements within the
CsAAO promoters. The computational analysis of microRNA target transcripts suggested that
CsAAO9 may be a target of csi-miR156. RNA-Seq data demonstrated high expression levels of
CsAAOs in roots and young fruits, while qRT-PCR analysis showed significant upregulation of six
CsAAOs in response to cold treatment. Furthermore, the activities of CsAAOs exhibited a pattern of initial decrease followed by an increase after exposure to low temperatures. These findings offer important insights into the role of
CsAAOs in response to cold stress. Furthermore,
AAOs could be target genes for breeding crops with better cold resistance.
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