The Apple Orthologs Of REVERSION-TO-ETHYLENE SENSITIVITY1 Putatively Interact With Members Of The NAC Transcription Factors

The Arabidopsis RTE1 (REVERSION-TO-ETHYLENE SENSITIVITY1) and its tomato ortholog GREEN RIPE (GR) are important in plant ethylene signaling, response and/or fruit ripening. To investigate the potential role of RTE1-like genes in apple (M. ×domestica Borkh.) fruit ripening, two orthologs of RTE1 were identified in the apple genome, designated MdRTE1a and MdRTE1b. Using yeast two-hybrid (Y2H) approach, a cDNA prey library was constructed from a pool of maturing/ripening fruits of ‘Golden Delicious’. Screening the library with MdRTE1a identified two putative NAC (NAM/ATAF1, 2/CUC2) proteins, designated MdNAC1 and MdNAC2, that interacted with MdRTE1a in yeast cells. MdRTE1b, a closely related paralog of MdRTE1a, was also confirmed to be interactive with MdNAC1 and MdNAC2 using the Y2H system. The expression of MdRTE1a and MdNAC1 was high in young fruits but low in more developed and ripening fruits. This pattern of low expression remained largely consistent and was not affected by treatment with 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception, or ethephon, an ethylene releasing compound. However, the expression of MdRTE1b and MdNAC2 rapidly increased during fruit ripening and was highly inhibited by 1-MCP. These data suggested that MdRTE1a, MdNAC1 and their possible interactions in apple cells may play roles in growth, whereas MdRTE1b, MdNAC2 and their putative interactions are involved in ethylene signaling, response and fruit ripening. The possible interactions between an RTE1-like protein and a NAC protein in plant cells are currently being investigated as such interactions have not been reported thus far.