| Feizixiao litchi (Litchi chinensis Sonn. cv. Feizixiao) is one of the most important early-maturing varieties in China, but the "stay green" phenomenon exists in litchi pericarp seems to affect the economic benefits. Feizixiao litchi adult trees were conducted to study the effect and molecular mechanism of pericarp corloration under Mg treatment. The trees were sprayed with Mg fertilizer, in paralel with clean water for control (CK). This research could enrich the development theory of litchi fruit, and help making rational fertilizationtechniques of Feizixiao litchi.The main results are as follows:(1) During fruit growth and development, the hue (h) value and the content of chlorophyll from Mg treatment and CK in pericarp showed a downward trend in general,the soluble sugar content in aril and the content of anthocyanin in pericarp showed an upward trend in general. The h value in Mg treatment was significantly lower than CK from 14 days to 24 days after treatment(day 14 to day 24), andthe content of anthocyanin in Mg treatment was significantly higher than CK at the same period. The differencesin contents of chlorophyll and soluble sugar were not significant. The results indicated that Mg treatment helped litchi pericarp turn red in advance by promoting the accumulation of anthocyanin, and overcome the "stag green" problem.(2) Content of abscisic acid (ABA), output of ethylene, activities of UDP-Glucose:flavonoid 3-O-glucosyltransferases (UFGT), pheophorbide a monooxygenase (PaO) and chlorophyllase (Chlase) showed an increasing trend during fruit growth and development.The content of ABA in Mg treatment was significantlyhigher than CK from day 17 to day 24, and the UFGT activity in Mg treatment was significantly higher than that of CK from day 14 to day 21. There was no significant difference in other indexes.The results indicated that Mg treatment promoted the anthocyanin accumulation in pericarp by increasing the content of ABA and activity of UFGT.(3) The pairwise correlations between the contents of anthocyanin and ABA, and the activity of UFGT in Mg treatment were significant, and the chlorophyll content was significantly negatively correlated with the output of ethylene, or activities of Chlase and PaO. The results suggested that Mg treatment might increase the activity of UFGT by increasing the content of ABA,which contributed to the synthesis of anthocyanin.Meanwhile, the higher ethylene production in the pericarp might increase the activities of PaO and Chlase, and accelerate the degradation of chlorophyll.The synthesis of anthocyanin and the degradation of chlorophyll contributed to red skin of litchi.(4) Mg treatment significantly improved the contents of water soluble Ca, total Mg and water soluble Mg. There was a mutual gain effect between contents of Ca and Mg,which promoted the accumulation of anthocyanin.(5) Illumina HiSeqTM 2500 and de novo were used for RNA samples sequencing andassembled and to establish a corresponding reference transcriptome. We generated 11.20 G nucleotides with Q20 of 98.52%. Trinity package assembled 50809 unigene with the average length of 735.47 bp, and N50 of 1304 bp. A total of 1226 unigenes were found to be differently expressed in the pairwise comparisons between any two periods of Mg-treated. 17 unigene of Mg treatment involved in flavonoid, anthocyanin biosynthesis pathway and ABA signal transduction pathway were identified. 15 unigenes were choosed randomly to conduct the Q-PCR analysis, and the veracity of RNA-seq was confirmed. The results indicated that Mg treatment might participate in the biosynthesis of anthocyanin by affecting the expression of these genes, and improve the color of Feizixiao litchi pericarp. |
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