Abstract:

Using the independently innovative grape variety ‘Yanniang No.1’ as the material, the FRO (ferric reduction oxidase) family genes were screened and cloned, and their bioinformatics identification and expression characteristics were analyzed. This study provides a theoretical basis for studying iron nutrition and the mechanism of absorption and utilization in fruit trees. In total, 6 FRO family genes were isolated from ‘Yanniang No.1’ by homologous cloning method, entitled by VvFRO1-VvFRO6, which belonged to the classic plant ferric reduction oxidase. The amino acid sequences of FRO proteins from 10 plants shared an overall identity of 43.66%, which were classified into 2 major groups (Groups I and II). VvFRO1-VvFRO3 belonged to Group I, while VvFRO4-VvFRO6 belonged to Group II. Phylogenetic tree analysis showed that VvFRO proteins were prone to be closely clustered with homologs form Citrus junos ‘Ziyang xiangcheng’ and Malus xiaojinensis, respectively. All VvFRO proteins were majorly localized in plasma membrane and contained 10-11 transmembrane domains (TMs). Quantitative real-time PCR (qRT-PCR) analysis showed that VvFRO3 was the most abundant expressed gene during different parts of ‘Yanniang No.1’ grape on the whole. VvFRO3 and VvFRO2 were highly expressed in leaves of both mature trees and seedlings, and VvFRO5 was highly expressed in fruits of hard core stage and veraison stage, while genes of VvFRO1, VvFRO4 and VvFRO6 were relatively lowly expressed. In addition, expression of FRO family genes in grape roots were easily induced by iron depletion, 200 mmol/L NaCl stress and 10% PEG6000 (w/v) stress, respectively, but changed little under low temperature (4℃) and heat (45℃) stresses. In particular, VvFRO3 in roots was upregulated under 200 μmol/L ABA treatment but down-regulated under 500 μmol/L iron toxicity stress. This study laid a molecular foundation for revealing iron absorption and transport mechanisms in grape.

Key words: grape, Fe uptake, ferric reduction oxidase, abiotic stress, expression pattern