Mechanism Of Jujube Reddening Based On Transcriptome Sequencing

Winter jujuba(Zizyphus Jujuba Mill.cv.Winter jujube)is a unique fresh jujube variety in China.It is pop?lar with consumers for its crisp,juicy and rich nutrition.However,after harvest,the winter jujube is easy to lose water,soft wine,browning and decay.In 3-5 days at room temperature,the peel is easy to turn into whole red,and the flesh loses nutrients rapidly,which significantly affects the edible value and circ?lation quality of the jujube,and restricts its long-distance transportation,marketing and industrial development.At present,the storage of Winter jujube mainly focused on nutrition evaluation,ignoring the relationship between change of skin color and storage quality.In our research,with white ripening period(W-White),pre-harvest half red ripe(NR-Natural semi-Red)and post-harvest half red ripe(CR-Chilled semi-Red)jujube as materials,based on transcriptome sequencing data,combined with physiological and biochemical indicators,from the two aspects of pigment changing and browning,we analyzed the color difference and explored the redness mechanism of the skin of Winter jujube jujube in different periods before and after harvesting.The res?lts will In order to provide a theoretical basis for the storage of Winter jujube jujube.Transcriptome analysis showed that there were a large number of differentially expressed genes in white ripe stage,semi-red ripe before harvest and postharvest.Combined with KEEG enrichment analysis of pigment-related metabolic pathways,it was found that the degradation of chlorophyll and the biosynthesis of carotenoid and flavonoid were associated with the red changing of winter jujube.There were significant differences in the expression of anthocyanin synthase gene(ANS)and quercetin synthase gene(FLS)during redness.The expression level of FLS gene in the postharvest semi-red ripeness was higher than the natural semi-red ripeness and white ripening period,while the expression of ANS in the natural semi-red ripeness and postharvest semi-red ripening stage was significantly higher than that in the white ripening stage.Combined with GO enrichment analysis of oxidation-related metabolism,it was found that the membrane lipid peroxidase gene showed a high expression trend in CR jujube,but the expression of the genes related to oxidation resistance,energy conversion and proton gradient was lower in the CR period.In addition,the expression level of PPO after harvest is lower than that before harvest.The res?lts of quantitative PCR showed that the transcriptome data were reliable.Pigment analysis showed that the main pigment substance in the peel of winter jujube were chlorophyll,carotenoids,naringenin,catechins,quercetin.Quercetin and anthocyanin were the main pigments that promote red change during the transition from white ripe to semi-red ripe before harvest.Anthocyanin was the main pigment promoting the change of red jujube from white ripe to semi-red ripe during postharvest storage.The difference was caused by the peak expression of flavonoid synthase gene(FLS)before harvest,which led to the accum?lation of quercetin and promoted the red change.After harvest,the FLS expression peak was delayed due to low temperature,and quercetin content was relatively low.However,low temperature has no obvious inhibitory effect on ANS,which leads to a large accum?lation of anthocyanins in the postharvest semi-red ripeness,which is a key pigment to promote the redness of the postharvest semi-red ripe winter jujube.The specific gravity of semi-ripe red pigment before harvest was higher than that after harvest.The browning analysis res?lts showed that the browning of semi-red jujube after harvest was more serious than that before harvest,and the quinone substance accum?lated obviously.Enzyme activity and total phenol content had certain influence on the browning of winter jujube peel,but the correlation was not strong.The main reason for the difference in browning was the damage to the cell structure of postharharvest jujube caused by low temperature stress.The mechanism was follows:in vitro stress and low temperature lead to increased membrane peroxidation,cell deformation,and severe lignification triggering anaerobic respiration,breaking the cell interval,and direct contact between enzymes and substrates led to browning.In addition,when the cuticle was damaged and peeled off,and accelerated water loss of the pericarp will also lead to the collapse of the pericarp structure,further accelerated browning,causing the brightness of the peel to decrease and the color to become dark.The quality analysis res?lts showed that: under the condition of small color difference,the indexes of semi-red ripe winter jujube before harvesting were better than those after post-harvest ripening.