Genome-wide identification and expression analysis of the citrus GRF family reveals CsGRF8 as a positive regulator of color transformation
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Background Growth regulating factors (GRFs) are a family of plant-specific transcription factors that play key roles in the regulation of plant growth and development. However, to date, there has been no in-depth studies on GRF genes or their roles in Citrus plants, with or without an interstock. Here, we investigated the effects of the interstock on fruit development in ‘Harumi’ tangor cv. and GRF -related genes. Our study of fruit development characteristics revealed that, at 180 days after flowering, the weight of ‘Harumi’ tangor ( ‘Harumi’ tangor cv. ) / Hongjv ( Citrus reticulata ) combination, (HP), fruit was significantly larger than that of ‘Harumi’ tangor / Navel orange ( Citrus sinensis Osb. var. brasliliensis Tanaka) / Hongjv combination, (HPP), while the color of the external peel of HPP turned orange 30 days before that of HP. We isolated nine CsGRF genes from the citrus genome (GCF_000493195.1), whose physicochemical properties, gene structure, conserved domains, conserved motifs, and phylogenetic relationships were determined using bioinformatics analysis. Additionally, we analyzed their expression in the flowers, leaves, pericarps, capsules, and juice sacs. Results All nine CsGRF genes were expressed at low levels in the scion flowers. Particularly, the expression levels of CsGRF2 were remarkably higher in HP than that in HPP pulp, whereas those of CsGRF5 were significantly higher in HPP than in HP pulp, suggesting their distinct roles in regulating fruit development. In the transient transformation of strawberries, overexpression of CsGRF8 can promote the color transformation of strawberries at white ripening stage, but inhibit the ripening of strawberries at the color-break stage. Conclusions Our study explored the genome-wide identification, characterization, and possible relationship between fruit development and expression profile of the CsGRF gene family in ‘Harumi’ tangor.
