The Signal Transduction Mechanisms Of Protein Kinase FERLs/SnRK2s In The Regulation Of Fruit Ripening

Regulation of fruit development and ripening is one of the most important questions in pomology science. For many years,a large number of researches were carried out around fruit development regulation mechanisms. However, it's still unclear about the upstream signal transduction mechanism,that is, the profound mechanism in manipulating physiology, biochemical metabolism or structural gene,because most researches were confined to the physiological, biochemical or structural genes. This paper used apple and strawberry as test materials, the model plant of climacteric and non-climacteric species,respectively, and used FERONIA-like Receptor Protein Kinase (FERLs) and Sucrose non-Fermenting Protein Kinase 2s (SnRK2s) as the entry point, studied the signal transduction mechanism in regulating fruit development and ripening of climacteric and non-climacteric species. The major results are summarized as follows:1. Bioinformatics analysis identified six members of FERLs in strawberry. Analysis for the spatio-temporal expression of FERLs, we found a FERL member,named FaMRLK47(FaFERL1), is closely correlated to fruit development and ripening. Overexpression and RNAi-mediated downregulation of FaMRLK47 delayed and accelerated fruit ripening, respectively. These suggest that FaMRLK47 may play an important role in strawberry fruit development and ripening. Further analysis showed that FaMRLK47 physically interacts with FaABI1,a negative regulator of abscisic acid (ABA) signaling, and demonstrated that FaMRLK47 regulates fruit ripening by modulating ABA signaling, in accordance with these findings,overexpression and RNAi-mediated downregulation of FaMRLK47 caused a decrease and increase,respectively, in the ABA-induced expression of a series of ripening-related genes. These results suggest that FaMRLK47 controls strawberry fruit development and ripening by regulating ABA signal transduction.2. Bioinformatic analysis indicated that the apple genome contains 17 members of the FERLs family.Analysis for the spatio-temporal expression of FERLs, we found two FERL members, MdFERL1 and MdFERL6, is closely correlated to fruit development and ripening. Heterologous expression of MdFERL6 or MdFERL1 in tomato (Solanum lycopersicum) , fruit delayed ripening. virus-induced gene silencing (VIGS) of SIFERL1, the tomato homolog of FER, promoted tomato fruit ripening. Further analysis showed that overexpression and antisense expression of MdFERL6 in apple fruit calli inhibited and promoted ethylene production, respectively. These results suggest that MdFERL1 and MdFERL6 are negative regulatory in apple fruit development and ripening. BiFC and Co-Immunoprecipitation experiments all demonstrated that both MdFERL6 and MdFERL1 physically interacted with MdSAMS(S-adenosylmethionine synthase),a key enzyme in the ethylene biosynthesis pathway. Overexpression of MdFERL6 can inhibited the activity and gene expression of SAMS. All these results strongly indicated that MdFERL1 and MdFERL6 controls fruit development and ripening by regulating ethylene biosynthesis.3. Bioinformatics analysis identified nine members of SnRK2s,named MdSnRK2.1?2.9 in apple.Gene expression analysis found that two members of the MdSnRK2s family, MdSnRK2.4 and MdSnRK2.9 may play important roles in the regulation of apple fruit ripening. Expression of MdSnRK2.4 and MdSnRK2.9 in apple fruit callus and tomato fruits found that MdSnRK2.4 and MdSnRK2.9 could induce mannitol and ABA-mediated ethylene production. In-depth study shows that MdSnRK2.4 and MdSnRK2.9 could physically interact with MdHB1/HB2, regulating the expression of ethylene synthesis key enzymes, and regulate the transcriptional activation and protein stability of MdHB1 and MdHB2 through phosphorylation of MdHB1/2 under adverse conditions such as ethylene in the fruit synthesis, thus affecting the fruit ripening.Collectively, FERLs and SnRK2s can manipulate the production of ethylene in climacteric fruits and control ABA signal transduction in non-climacteric fruits. Previous studies have shown that ethylene and ABA are key signals for the maturation of climacteric and non-climacteric fruits, respectively. Therefore,this study has an important role in our understanding of the development and ripening of climacteric and non- climacteric fruits, but also laid the theoretical basis for systematically revealing the signal transduction mechanism of fruit development and mature regulation.