| Fruit cracking is a serious problem in tomato production.It can contribute to serious economic losses to the growers and sellers,because it can speed up the loss of fruit water,shorten the storage and transportation time,easily get disease,seriously decrease the appearance of quality and commodity value.Fruit cracking is a quantitative trait(QTL).It is controlled by many genes.So far,no gene for tomato fruit cracking resistance has been fine-mapped or positionally cloned,because the genetic mechanism of tomato fruit cracking is extremely complicated.Therefore,the fine-mapping of gene for tomato fruit cracking,not only help to clarify the molecular mechanism of tomato fruit development,but also to guide tomato breeding for fruit cracking resistance.In this study,we identified a line,whose fruits with epidermal reticulation(ER),from an introgression line population of Solanum pennellii(LA0716)in a fresh market tomato inbred line.And then,we observed the phenotype of ER fruits through paraffin and scanning electron microscopy,narrowed down the region of ER4.1 gene by fine-mapping,and analyzed the transcriptome of fruit peel from ER and WT(wild type)which based on the RNA-seq data.The main results are summarized as follows:1?The peels of ER fruits initially appeared fissure at 23 DAP,and then was characterized by epidermal reticulation at mature green stage.Therefore,it belonged to Cuticle Cracking(CC).Staining with the dye Sudan IV revealed that the thickness of the outer cuticle increased gradually with fruit development,but a similar thickness was observed in the ER and WT fruits at all the stages examined.The ER fruit was seriously dehydrated mainly because the ER cuticle was fracturing and uncontinuum.2?The trait of ER fruit was identified to be controlled by a dominant locus through genetic analysis.The ER4.1 gene was initially mapped to the distal end of chromosome 4 by used the whole genome molecular marker.To further narrow the interval of ER4.1,4400 individuals were used for fine mapping,Finally,ER4.1 was fine mapped to a ~300 kb region between markers InDel 4-82 and the distal end of chromosome 4.The region may be characterized by recombination suppression.According to the tomato genome annotation(ITAG2.40,https://solgenomics.net/),a total of 52 hypothetical genes were predicted in this region.3 ? Based on RNA-seq data and their putative molecular function,Solyc04g082540,Solyc04g082950,Solyc04g082630 and Solyc04g082910 were suggested to be potential candidate genes for the ER4.1 locus.4?Comparison of the transcriptomes of fruit peel between ER and WT at two time points,15 DAP and 23 DAP,a total of 4478 differentially expressed genes(DEGs)were detected in at least one of the time points between ER and WT peel,using a rigorous p value cut-off(? 0.01).At 15 DAP and 23 DAP,2720 and 2621 DEGs were identified in ER exocarp,respectively,compared with the WT fruit,and 863 DEGs were identified at both two time points from ER fruit peel than WT.To identify significantly altered biological processes associated with the DEGs in the ER fruit from the two stages,we carried out a Gene Ontology(GO)enrichment analysis.The DEGs were enriched in ‘respond to hormone',‘photosynthesis',‘stress response' and ‘metabolic process'.In addition,the transcriptome analysis revealed that the expression levels of genes involved in cutin,wax and flavonoid biosynthesis were altered in the ER fruit compared with WT fruit.Genes reported to contribute to the synthesis of alkanes and triterpenoid were all more highly expressed at 15 DAP in the ER fruit peel than that in WT fruit peel.In contrast,gene is required for the synthesis of primary alcohols,was expressed at lower levels at this time point.The expression levels of genes encoding chalcone synthase(CHS)were higger in ER fruits at 15 DAP.Genes involved in rutin synthesis were up-regulated in ER fruit.In this paper,the phenotypic characterization,fine mapping and transcriptome analysis of ER fruit in tomato may be favourable for tomato fruit quality breeding. |
PDF Full Text Request