Study On Molecular Mechanism During Riping Of Melons (Cucumis Melo L.) With Different Textural Properties

The germplasm resources of melon are rich,and the textural property is an important indicator for the quality and marketability of the fruit,since the texture of different varieties of melons are different.However,there is no system on evaluation of melon flesh so far,and the molecular mechanism during riping of non-climacteric melon is also unknown.In this study,three types of melons were used to establish an evaluation system of melon flesh,and textural properties of melo germplasm were also tested.Besides,among thin-skinned melons,P10 with hard flesh and 417 with crispy flesh were selected to test the transcriptome sequencing.Molecular mechanisms on ripening of melons with different texture were analyzed,and the main results as follows:1.Textural properties of melon flesh from three types were investigated by three kinds of textural analysis methods: texture profile analysis(TPA),puncture and shear method.The results showed that five parameters,including hardness,adhesiveness and chewiness obtained by TPA,the brittleness and average hardness obtained by puncture method,could indate different texture of melon flesh.Therefore,TPA and puncture method could be used to evaluate textural properties of melon flesh.While shear method couldn't characterize the textural properties of melon flesh accurately.Melon showed crispy characterization with hardness ranging from 1437.78 to 3047.08 g,adhesiveness ranging from-6.37 to-10.65 g·s,chewiness ranging from 205.20 to 520.54 g,brittleness ranging from 3.10 to 6.78 N/s and average hardness values of puncture ranging from 1.26 to 2.41 N,respectively.2.TPA and puncture methods were used to evaluate 108 melon fruits with differernt types.The results showed that hardness and brittleness of Yangjiaocui-type were within the above range and they were crispy;P10 and 725 had the biggest hardness(5513.39 g and 4157.40 g,respectively)and the biggest brittleness(7.77 N/s and 5.18 N/s,respectively)of thin-skinned melons and thick-skinned melons respectively,and their taste was hard.417 and 726 had similar genetic background with P10 and 725,but their hardness(1746.55 g and 1653.13 g,respectively)and brittleness(2.88 N/s and 2.50 N/s,respectively)were at middle level and they were crispy.Cha was a typical climacteric fruit,and it would be soften when it was ripe,compared with immature period,hardness and brittleness after mature could decreased to 9% and 20% respectively.Sections of flesh tissue at three different mature stages of these materials were made.The results showed that smaller cells and dense arrangements led to upper flesh hardness no matter it is thin-skinned or thickskinned,and it had smaller changes during riping.On the contrary,it could lead to lower flesh hardness,and had bigger changes.3.High-throughput sequencing technology was applied for transcriptome sequencing(RNA-seq).Different maturity periods of P10 and 417(with similar genetic background)were tested,then total output was 40.25 Gb Clean Data,assembly total Unigene was 28,388,total length was 27,396,979 bp,and N50 was 1,404 bp.Different expressed genes were identified,and functional annotation and enrichment analysis were conducted.Expansin family genes were screened from different expressed genes.4.Real-time PCR of expansin genes showed the same variation trend with the results obtained by sequencing data.The results showed that expression of CmEXP1,CmEXP3 and CmEXP4 at different stages of 417 were significantly different.And they had the same trend: increased firstly,then decreased and expression at mature stage was the highest,the hardness and brittleness during mature period decreased to 52.8% and 56.3% respectively.The results indicated that these genes played a regulatory role in texture formation of crispy characterization and fruit ripening.Expression of CmEXP2 at different stages of P10 was significantly different: increased at first,then decreased and expression at mature stage was the highest,compared with immature period,the hardness and brittleness during mature period could increase to 1.4 and 1.1 times respectively.Results indicated that CmEXP2 played a regulatory role in the formation of hard flesh and in the maintenance of the hardness.