Ferritin plays an important role in plant growth and development, and its biological function in fruit trees are essentially unknown. Cloning of grape Ferritin family genes and revealing their expression patterns at different fruit developmental stages and their response differences to foliar spraying of amino acid iron (Fe) compound fertilizers could provide a theoretical basis for studying the molecular mechanisms of Fe nutrition and metabolism in fruit trees.

The Ferritin family genes were screened and identified in grape genome by homologous cloning. The detailed characteristics of Ferritin genes and their encoded proteins were analyzed by using bioinformatical methods. The tissue-specific expression patterns of Ferritin family genes during distinct fruit developmental stages and differential response to foliar spraying of amino acid-iron compound fertilizer were determined by carrying out real-time fluorescent quantitative PCR.

In total, 4 Ferritin family genes were retrieved and cloned from grape, entitled with VvFer1-VvFer4, which were distributed on No. 6, 8 and 13 chromosomes, containing 7 introns with different lengths. VvFer proteins were mainly located in chloroplast and nucleus. The amino acid sequence identity of Ferritin homologs from 16 plant species was as high as 61.48%. Phylogenetic tree analysis indicated that Ferritin homologs belonging to the same genus, such as Arabidopsis and turnip of Cruciferae, tobacco and potato of Solanaceae, soybeans, peanuts and chickpeas of Leguminosae, rubber trees, cassava and castor of Euphorbiaceae, and apples, peaches and strawberries of Rosaceae, possessed a closer genetic distance during evolution. Grape VvFer3 was closely clustered with Solanaceae homologs. The expression levels of VvFer genes were different among distinct tissues or organs of 5-year-old Mathelan grape trees during different fruit developmental stages. In particular, the expression level of VvFer3 was the most abundant, and the maximum expression was observed in fruits from hard core stage to mature stage, followed by VvFer2 and VvFer4. The content of Fe Marselan fruits was slightly different among distinct grape developmental stages, which was gradually increased from young fruit stage, and reached the highest value at veraison stage, and then slightly decreased until mature stage, but still higher than that of young fruit stage and hard core stage. Foliar spraying treatment significantly enhanced Fe content of fruits at mature stage, accompanied by ACO (aconitase), NIR (nitrate reductase) and SDH (succinate dehydrogenase). Genes of VvFer2-4 were significantly up-regulated by foliar spraying of amino acid-iron compound fertilizer, which was closely related to distinct grape tissues/organs and different fruit developmental stages. In details, the expression of VvFer2 in fruits was sensitive to foliar spraying treatment during the whole period of grape development. The expressions of VvFer3 in all tested tissues were sensitive to foliar spraying treatment from young fruit stage to veraison stage. The expressions of VvFer4 in phloem and leaves were continuously induced by foliar spraying treatment during the whole period of grape development, whereas in fruits from young fruit stage to veraison stage. The expression of VvFer1 was relatively low, but very uniform, and there was no response to foliar spraying treatment at the transcription level.

Four Ferritin family genes were cloned and identified in grape, whose expression were significantly different among distinct tissues during different fruit developmental stages and were prone to be up-regulated under foliar spraying treatment of amino acid-iron compound fertilizer. The overall expression level of VvFer3 gene was the highest in all tested tissues (especially in fruits) during the whole fruit development stage, and was up-regulated in fruits under foliar spraying treatment from young fruit stage to the verason stage.