Effects And Mechanisms Of Auxin And Auxin-ethvlene Interaction In The Regulation Of Tomato Fruit Ripening

Tomato ripening is a complex and highly coordinated process,which is under the regulation of many plant hormones.Ethylene regulation during tomato fruit ripening has been well documented.However,the molecular mechanism of auxin regulation during fruit ripening and how auxin-ethylene crosstalk network modulate ripening process is still not very clear.So we treated postharvest mature green cherry tomato fruit with auxin or ethephon and investigated the short-term and long-term effects of auxin on tomato fruit ripening process,pigment metabolism,primary metabolite profiling and auxin-ethylene interaction.The results are summarized as follows:1.Auxin treatment up-regulated the expression of auxin response genes(15 AUX/IAA genes,4 GH3 genes and 1 SAUR genes),GST-encoding genes and stress tolerance-related TF genes and induced the recruitment of a large number of defense-associated genes to improve stress resistance,reduce the stress of high-level auxin,and maintain auxin homeostasis.During the subsequent period,auxin enhanced the transcript levels of the genes involved in system 1 ethylene synthesis and maintained the high methylation level in the nucleus to repress the expression of system 2 ethylene synthesis-related genes.Finally,the expressions of the genes associated with carotenoid metabolism,cell wall degradation and energy metabolism were strongly repressed,and the ripening process was retarded.Additionally,the expression patterns of the genes involved in ethylene biosynthesis and signal transduction were markedly disturbed by exogenous auxin.The results of correlation network analysis revealed a strong correlation between auxin-and ethylene-related genes,suggesting significant crosstalk between auxin and ethylene during tomato ripening.2.Exogenous auxin strongly interfered the accumulation and conversion of pigment,total phenolics and flavonoids but might not quite influence the final content of these compounds in full ripe tomato fruit.Transcript analysis revealed that the regulation on genes expression by exogenous auxin was more violent at early and middle stage of ripening process compared with the weak effects of auxin at late ripening stage.The results of expression profiling of ripening-related transcription factor genes revealed that SIRIN,SICNR,SIGLK2,SIARF4 and SlAP2a might participate in the regulation of pigment metabolite of auxin except SlGR.3.Dramatic changes on the content of amino acids,sugars and organic acids were induced by auxin during tomato ripening period and the alterations were not able to be completely restored at the end of ripening.The contents of citric acid,threonic acid and succinic acid were increased in auxin-treated fruit whereas alanine and aspartic acid accumulation was repressed by exogenous auxin.4.Ethylene modulated auxin transport,metabolism(ACS2,ACS4,ACS6 and 6 ACO genes)and signaling processes(ETR genes,EBF genes and ERF genes)by affecting the expression patterns of genes encoding auxin carrier proteins,aldehyde dehydrogenase and primary auxin-responsive proteins.Most genes involved in ethylene biosynthesis and signaling were regulated at 7 days after treatment with exogenous auxin.Furthermore,the expression levels of mitogen-activated protein kinase(MAPK)and of ubiquitination-related genes were altered in auxin-treated fruit,suggesting that auxin regulates ethylene metabolism and signaling via complicated mechanisms.The potential interaction points in auxin-ethylene crosstalk were also identified by different expression analysis of the genes regulated by both auxin and ethylene treatment and ethylene and a model was proposed.Our analyses provide a global insight into the ethylene-auxin interaction and predict the potential regulators in the crosstalk of the two hormones during the fruit ripening process.