Identification and functional characterization of APRR2 controlling green immature fruit color in cucumber (Cucumis sativus L.)

Our previous studies have found that gene APRR2 is the candidate gene of w controlling the green color of immature fruit in cucumber, and its allele aprr2, which controls the white color, has a 101-amino acid residues deletion at the C-terminus compared with APRR2. Here, we characterized the APRR2 and analyzed its function in cucumber. qPCR analysis and prokaryotic expression of APRR2 and aprr2 clarified the relationship between APRR2 and aprr2 and confirmed that APRR2/aprr2 is a gene controlling cucumber color. Sequence and phylogenetic relationship analysis revealed that gene APRR2 and aprr2 with REC domain and DNA-binding B-motif are placed into subclass I of PRR subfamily. Subcellular localization assay indicated that APRR2 is a nuclear protein, but aprr2 is not. These results suggest APRR2 gene is a transcription factor in cucumber. Additionally, the expression analysis of Class-I KNOTTED1-like homeobox genesTKN4 and TKN2 involved in the chloroplast development showed they were in line with APRR2 expression, therefore, APRR2 together withTKN4, TKN2 likely contribute to the mechanisms related to chloroplast development.