Mitogen-activated protein kinase 14-mediated phosphorylation of MaMYB4 negatively regulates banana fruit ripening

Mitogen-activated protein kinase(MAPK/MPK)cascades play crucial parts in plant growth,development processes,immune ability,and stress responses;however,the regulatory mechanism by which MAPK affects fruit ripening remains largely unexplored.Here,we reported that MaMPK14 cooperated with MaMYB4 to mediate postharvest banana fruit ripening.Transient overexpression of individual MaMPK14 and MaMYB4 in banana fruit delayed fruit ripening,confirming the negative roles in the ripening.The ripening negative regulator MaMYB4 could repress the transcription of genes associated with ethylene biosynthesis and fruit softening,such as MaACS1,MaXTH5,MaPG3,and MaEXPA15.Furthermore,MaMPK14 phosphorylated MaMYB4 at Ser160 via a direct interaction.Mutation at Ser160 of MaMYB4 reduced its interaction with MaMPK14 but did not affect its subcellular localization.Importantly,phosphorylation of MaMYB4 by MaMPK14 enhanced the MaMYB4-mediated transcriptional inhibition,binding strength,protein stability,and the repression of fruit ripening.Taken together,our results delineated the regulation pathway of MAPK module during banana fruit ripening,which involved the phosphorylation modification of MaMYB4 mediated by MaMPK14.

Methionine oxidation and reduction of the ethylene signaling component MaEIL9 are involved in banana fruit ripening

The ethylene insensitive 3/ethylene insensitive3-like(EIN3/EIL)plays an indispensable role in fruit ripening.However,the regulatory mechanism that links post-translational modification of EIN3/EIL to fruit ripening is largely unknown.Here,we studied the expression of 13 MaE IL genes during banana fruit ripening,among which MaE IL9 displayed higher enhancement particularly in the ripening stage.Consistent with its transcript pattern,abundance of MaE IL9 protein gradually increased during the ripening process,with maximal enhancement in the ripening.DNA affinity purification(DAP)-seq analysis revealed that MaE IL9 directly targets a subset of genes related to fruit ripening,such as the starch hydrolytic genes MaA MY3D and MaB AM1.Stably overexpressing MaE IL9 in tomato fruit hastened fruit ripening,whereas transiently silencing this gene in banana fruit retarded the ripening process,supporting a positive role of MaEIL9 in fruit ripening.Moreover,oxidation of methionines(Met-129,Met-130,and Met-282)in MaEIL9 resulted in the loss of its DNA-binding capacity and transcriptional activation activity.Importantly,we identified MaEIL9 as a potential substrate protein of methionine sulfoxide reductase A MaMsrA4,and oxidation of Met-129,Met-130,and Met-282in MaEIL9 could be restored by MaMsrA4.Collectively,our findings reveal a novel regulatory network controlling banana fruit ripening,which involves MaMsrA4-mediated redox regulation of the ethylene signaling component MaEIL9.

The association of HpDof1.7 and HpDof5.4 with soluble sugar accumulation in pitaya fruit by transcriptionally activating sugar metabolic genes

Soluble sugar is one of the most important factors affecting fruit flavor and quality.Here,we report the identification of two Dof(DNA-binding with one finger)transcription factors termed HpDof1.7 and HpDof5.4 and their roles in influencing sugar accumulation in pitayas.HpDof1.7 and HpDof5.4 share a similar expression pattern with sugar metabolism-related genes HpSuSy1 and HpINV2,and sugar transporter genes HpTMT2 and HpSWEET14 during pitayas maturation,and their expression pattern was also consistent with the accumulation of glucose and fructose,which were the predominant sugars in pitayas.HpDof1.7 and HpDof5.4 were both typical nucleus-localized proteins with trans-activation ability.Gel mobility shift assay revealed that HpDof1.7 and HpDof5.4 were bound to promoters of HpSuSy1,HpINV2,HpTMT2 and HpSWEET14.Finally,transient expression assays in tobacco leaves showed that HpDof1.7 and HpDof5.4 increased the activities of HpSuSy1,HpINV2,HpTMT2 and HpSWEET14 promoters,thus facilitating sugar accumulation by transcriptionally enhancing sugar metabolic pathway genes.Our findings provide a new perspective on the regulatory mechanisms of Dof transcription factors in sugar accumulation and pitaya fruit quality formation.