Mechanism For The FaMAPK6/FaMYB44.2 Signaling Module Regulating FaSPS3,a Key Gene Of Sucrose Synthesis

Fruit ripening and quality regulation are one of the key issues in fruit tree research.Fruit ripening and quality formation are complex biological processes regulated by many factors and involve multiple metabolic systems.The molecular basis of regulation is a sophisticated and complex cellular signal transduction network.Identifying and elucidating the function of key signaling proteins in fruit ripening and quality formation provides a good entry point and breakthrough for us to reveal fruit ripening and quality formation.Strawberry is an important horticultural crop.Due to its important economic value and unique botanical characteristics,strawberry has become a model material for studying fruit ripening and quality regulation.In this study,Octoploid strawberry(Fragaria × ananassa Ducherne,cv Benihoppe)was used as experimental material,and the research on signal transduction mechanism was taken as the entry point.The research on the quality formation of strawberry fruit,especially the signal transduction mechanism of sugar and acid metabolism regulation,was carried out in-depth systematic research.The main results are as follows:1.Based on bioinformatics analysis,we identified three FaMYB44 family members in the strawberry genome.The expression of FaMYB44.2 is closely related to strawberry fruit ripening.Transient manipulation of FaMYB44.2 in strawberry fruit can regulate the accumulation of soluble sugar and malic acid and regulate the expression of related structural genes.Further studies showed that FaMYB44.2 mainly affects the sucrose accumulation of strawberry fruit by regulating the expression of the key gene FaSPS3(Sucrose phosphate synthase 3,SPS3).The regulation of FaSPS3 by FaMYB44.2 is closely related to the transcription factors FabHLH3 and FaMYB10.FaMYB10 is a key transcription factor involved in regulation of anthocyanin accumulation in strawberry fruit.The transcriptional level of FaMYB10 is significantly increased in white fruit.The high expression of FaMYB10 inhibited the expression of FaMYB44.2,and formed a competitive advantage in the interaction with FaMYB44.2 co-repressor FabHLH3,while FabHLH3 interacting with FaMYB10 was transformed into an activator,and FaMYB10 synergistically activates the expression of FaSPS3,thereby regulating the accumulation of sucrose in strawberry fruit.2.To further reveal the signal transduction mechanism of FaMYB44.2-mediated strawberry fruit ripening,we explored its upstream signal components.Previous studies have shown that MAPK and MYB play an important role in plant development and stress response through MAPK-MYB signal module,but whether this signal module can participate in the regulation of fruit quality formation,its specific signal members are all unclear.To this end,we identified MAPK family members in strawberry genome and analyzed their interaction with FaMYB44.2.It was found that there were 12 MAPKs family members in the strawberry genome,and FaMAPK6 interacted strongly with FaMYB44.2 protein,suggesting that it may be closely related to the function of FaMYB44.2.Transient overexpression or silencing of FaMAPK6 in fruits can promote or delay the coloration of strawberry fruit,alter fruit firmness,anthocyanin content,flavonoid content and aroma components,and regulate the expression of related structural genes involved in cell wall metabolism,pigment synthesis,aroma accumulation,soluble sugar and titratable acid metabolism.To explore whether FaMAPK and FaMYB44 can participate in FaSPS3-mediated sucrose accumulation,we verified by Effector-Reporter system,we found that FaSPS3 promoter activity was significantly inhibited when FaMYB44.2 was transformed alone.When FaMAPK6 and FaMYB44.2 were co-transformed,the inhibition effect was significantly enhanced.When co-transformed FaMKK4,FaMAPK6 and FaMYB44.2,the inhibition effect was further enhanced.The above results showed that the 'FaMKK4-FaMAPK6-FaMYB44.2' signaling module was involved in the regulation of FaSPS3 function,which in turn affected the sucrose accumulation of strawberry fruit.In addition,we also found that FaMAPK6 interacts with FaMYB10 and FaJAZ1.3.We also found that FaMYB44.2 and FaMAPK6 are involved in the regulation of jasmonic acid(JA)signaling in strawberry fruit development and quality formation,suggesting that there are multi-signal system synergy and cross-talk mechanism in strawberry fruit quality regulation.Taken together,this study demonstrates that FaMYB44.2 is a negative regulator of sucrose accumulation in strawberry fruit,and is involved in jasmonic acid-mediated regulation of sucrose accumulation in strawberry fruit;FaMAPK6 regulates the formation of strawberry fruit quality and regulates FaSPS3 via the'FaMKK4-FaMAPK6-FaMYB44.2' signal module.These results laid a theoretical foundation for the in-depth analysis of the mechanism of strawberry fruit ripening and quality formation.