Study On The Mechanism Of Auxin Alleviating The Occurrence Of Tomato Locules Malformed Fruit Under Night Low Temperature

Tomato（Solanum lycopersicum L.）is the crop with the largest planting area in facility vegetable production in China.However,the low night temperature stress in autumn,winter or early spring is easy to lead to a large number of multi-locule malformation of tomato,which seriously affects the appearance quality and commodity value of tomato,and has become one of the important factors to reduce the benefit of facility tomato.The multi-locule malformation of tomato is mainly caused by the abnormal development of carpel during flower bud differentiation.Previous studies have shown that auxin substances can reduce the incidence of malformed fruit and inhibit the formation of tomato locules,while the role of auxin transport inhibitor（TIBA）is an auxin type of substance that inhibit auxin transport,but its effect is just the opposite,but the mechanism of how auxin maintains the number of tomato locules by coordinating the hormone balance in the shoot tip is not clear.In this study,the medium and large fruit tomato’Zhongshu No.6’was used as the test material to analyze the changes of different hormone contents in the shoot tip after treatment with NAA and TIBA.Combined with transcriptome analysis,the genes that auxin may affect the formation of tomato ventricle were preliminarily screened,and the possible mechanism of auxin to alleviate the multi locules malformation of tomato at night was discussed.The main results of this paper are as follows:In this study,the medium and large fruit tomato’Zhongshu No.6’was used as the test material to analyze the changes of different hormone contents in the shoot tip after treatment with auxin and auxin transport inhibitors.Combined with transcriptome analysis,the genes that may affect the formation of tomato ventricle were preliminarily screened.To explore the metabolic pathways involved in the regulation of tomato locules formation by NAA.The main results of this paper are as follows:1.By spraying auxin NAA and auxin polar transport inhibitor TIBA at different concentrations,the number of locules in tomato fruit was observed.The results showed that the number of locules in fruit treated with NAA decreased,and TIBA could significantly increase the number of locules in tomato fruit.It is further confirmed that NAA can reduce and slow down the occurrence of abnormal fruit,and TIBA can significantly promote the occurrence of multi-locule abnormal fruit.2.The contents of auxin,gibberellin and cytokinin hormones in the shoot tips of tomato seedlings treated with NAA and TIBA were determined by liquid chromatography-mass spectrometry.Compared with TIBA treatment,the contents of endogenous active auxin decreased and the contents of tryptamine and tryptophan increased under NAA treatment;The contents of active gibberellin GA₁,GA₄and its synthetic precursor GA₅₃decreased significantly;The contents of dihydrozeatin-7-glycoside（DHZ7G）,isopentene adenine nucleoside（IPR）,6-benzylamino-7-beta-d-glucopyranopurine（BAP7G）,zeatin nucleoside（TZR）and 6-Benzylaminopurine（BAP）of cytokinins decreased significantly.The above results showed that NAA significantly reduced the contents of active gibberellin and cytokinin.3.Through transcriptomic,the expression levels of hormone metabolism and signal transduction related genes treated with NAA and TIBA were analyzed.After exogenous application of NAA,the content of endogenous hormones was reduced by regulating the expression of differential genes YUCCA11,YUCCA14,ga2ox7 and CKX4,while the expression of ARR was down regulated,which affected the stem cell activity of stem meristem and reduced the locules function of tomato;In addition,the administration of TIBA resulted in the increase of active endogenous hormone content,up-regulated ARR gene expression and up-regulated WUS gene expression,stem tip overdevelopment leads to locules hyperplasia.