Study On The Relationship Between Endogenous Hormone Changes And Color During The Development Of Citrus Fruits

The appearance quality of citrus fruits is one of the most important factors affecting their economic value,and the diversity of fruit color is mainly due to the difference between carotenoid content and components.In terms of production,citrus fruits of the same species often have problems such as poor coloration and uneven greening during the ripening process.At present,the treatment with growth regulators can improve the coloration degree and coloring of fruits,but there are still problems such as poor selection of regulator types,side effects or failure to achieve the expected treatment effect.We speculate that during the process of fruit coloration and ripening,endogenous hormones may be the intrinsic cause of the difference in color and lust of different varieties of citrus,and there is an important relationship between the color presentation of the fruit.Based on this,Newhall navel orange(Citrus sinensis Osbeck cv.Newhall),satsuma mandarin(C.unshiu Marc),W.Murcott tangor(C.spp)and Kaopan pummelo(C.maxima)were used as experimental materials for the analysis of the color changes of fruits and the dynamic changes of carotenoids and hormones in different tissues during the process of development to maturity.It is finally determined that the hormone types is most related to fruit color.Transcriptome sequencing was combined to explore and verify the expression changes of key functional genes in the hormone and carotenoid metabolic pathway,and the relationship between endogenous hormones and the color in citrus fruits was preliminarily clarified.This research will further explore the relationship between citrus fruit ripening and hormones,as will help understanding the coloration mechanism for technological innovation for citrus fruit quality improvement.1.Endogenous hormone and carotenoid accumulation varied in different citrus varieties.(1)There were obvious differences in the carotenoid components accumulated in four cultivars of citrus fruits: Newhall and W.Murcott have high specific accumulation of of β-citraurin in the peel,but,Satsuma mandarin and Kaopan pummelo mainly accumulated lutein and violaxanthin in the peel.Satsuma mandarin accumulated β-cryptoxanthin and zeaxanthin in the stage of yellow to orange,and the carotenoid accumulation of Kaopan pummelo was very low.The carotenoid components and contents of the pulp were less than their peel respectively in four cultivars.(2)Among the four cultivars,ABA,JA,JA-ILE and IAA were the most important hormones in the peel,which showed obvious differences in the development period and among different genotypes.The contents of endogenous ABA in the peel of Newhall and Kaopan pummelo were higher than that of W.Murcott and Wenzhou Mikan,both of which fluctuated significantly from the coloring stage(180 DAF);jasmonic acid content fluctuated less in the four cultivars,but JA-ILE not only showed differences in content,but also showed obvious inter-genotype differences in the change trend: Newhall and Kaopan pummelo fluctuated more than the rest two cultivars from the color change period.The types and contents of endogenous hormones in the flesh of the four citrus varieties varied greatly and were different from the peels,and all accumulated high levels of abscisic acid.2.The endogenous hormones most associated with the color of citrus fruits are abscisic acid(ABA)and jasmonic acid(JA).Based on the comparison of carotenoids and hormones,both the types of hormones and carotenoids in the peel are richer than that in the pulp.During the development process,endogenous hormone changes were concentrated in the greening stage,yellowing stage and ripening stage,which were related to the difference in fruit color and luster in different varieties,but the degree of correlation and effect were different.The results of the correlation analysis of peel hormones and carotenoids of four varieties showed that ABA was significantly related to the main accumulated carotenoids violasterin,β-limonin,β-cryptoxanthin,etc.,and jasmonic acid was also highly correlated with lutein,zeaxanthin and β-citraurin,among which JA-ILE was the active form of jasmonic acid and was also significantly related to the accumulation of major carotenoid components that present color.Abscisic acid and jasmonic acid are the hormones most related to color formation during citrus fruit ripening,and their anabolic and signal transduction pathways have important links with carotenoid metabolism.3.Combining transcriptome to identify differentially expressed genes from color breaking to mature at the gene level.We performed transcriptome analysis on the peel from the color-breaking stage to the ripening stage(160～220 DAF)in Newhall,for detecting differentially expressed genes before and after the color transition stage.GO analysis and KEGG pathway analysis were carried out on genes that were differentially expressed before and after the color transition period,cytochrome p450 pathway,hormone metabolism and signal transduction and carotenoid metabolism were identified,11 carotenoid-related genes and 40 hormonerelated genes were explored,and they were mainly enriched in abscisic acid,jasmonic acid,auxin and ethylene metabolism pathways.Combined with transcriptome data,real-time fluorescence quantitative verification of genes with higher content and obvious differences in the above metabolic pathways was performed,with the coloration and maturity of fruits,the important genes in carotenoid metabolism CCD4 b,ZEP,ZDS,LCYB2,PSY and NCED2 showed a high expression trend,and interspecific differences appeared in W.Murcott tangor,Satsuma mandarin,Newhall navel orange and Kaopan pummelo,which were consistent with the content of carotenoids.Abscisic acid-related genes Cs ABAs,AAO3,CYP707 As and jasmonic acid-related genes AOC,JAZs,AOS,LOX3,Cs PLIP,and JAR1＿4＿6 all showed developmental changes and obvious interspecific differences.Other signal transduction pathways and transcription factors were also expressed differently among cultivars and during development and fruit coloration,mainly after the colorbreaking period.Conclusion: It was revealed that the spatiotemporal dynamic accumulation law of the main color pigment carotenoids and hormones in the fruit and their correlation were revealed,and it was found that the levels of abscisic acid and jasmonic acid were most correlated with the color change of citrus fruit,and their metabolism and signal transduction-related genes showed significant differential expression from the coloration stage to the ripening stage of the fruit,and CYP707A2,JAZ1,PP2 C and HSP21 were more consistent with the corresponding hormones and carotenoids in the coloration process of citrus fruits,which could be used as bridge genes between the two.