Pericarp Development And Related Gene Screening Of Early Maturing Bud Variant Material Of ’Okitus Wase’ Satsuma Mandarin

The shoot selection is an important way for citrus genetic improvement and variety selection,and citrus fruit skin phenotype largely determines fruit appearance and storage and transportation resistance.Our group found an early maturing bud variant of‘Okitus wase’ satsuma mandarin whose bud ripening was about 30 d earlier than that of the parent plant.In this study,the phenotypes,related components and endogenous hormones of the peel of the mother and the early-ripening bud variant were determined dynamically during fruit growth and development,and the transcriptome was analyzed to investigate the mechanism of phenotype development of the early-ripening bud variant.The main results are as follows.The main findings were as follows:(1)The developmental processes of pericarp were different between the parent and early maturing bud variant materials at the same period.At the time of fruit expansion,the hardness of the peel of the early-ripening bud variant material decreased more rapidly,which may be mainly related to the decrease of cellulose and hemicellulose content;at the time of maturation of the early-ripening bud variant material,the parent material was still in the color change stage,and the total pectin,hemicellulose and lignin in the bud variant material were less,and the cellulose content was 168.98 mg/g,which was very significantly lower than that of the parent material.Carotene,α-carotene,β-carotene and violet xanthophyll content were all significantly higher than those of the parent material,and the oil cells were evenly distributed,uniformly developed,larger in size and spacing,with fewer oil cells per unit area,softer fruit,thinner and smoother skin,and more obvious coloration.(2)The four endogenous hormones may be related to the early ripening of the early maturing bud variant materials.ABA in the early maturing bud-change material rose sharply to 829.54 ng/g in the middle of fruit expansion,which was 2.04 times higher than that of the parent material in the same period,and ABA rose earlier and faster,and ABA was maintained at a higher level during both fruit expansion and color change,and the orange peel oil content was higher on August 9.In the middle of fruit expansion,IAA in the early maturing bud variant was significantly higher than that in the parent material,and ETH and BR in the peel reached their peak about 15 and 30 d earlier than that in the parent material,respectively.The high concentration of ABA at the early stage of fruit development may be the key to promote the early ripening and orange peel oil accumulation in the early maturing budding material,and the early fruit color change in the budding material may depend on the combined effect of high concentration of ABA,ETH and BR at the early stage of fruit development,while the effect of higher concentration of IAA on fruit ripening in the early maturing budding material needs to be further investigated.(3)The transcriptome sequencing results showed that there were 2051 and 2207 DEGs on July 10 and September 8,respectively,and more down-regulated DEGs than up-regulated DEGs,and the early maturing bud-variant material might promote early fruit skin development finally mainly by down-regulating key genes in these two periods and up-regulating key genes on August 9.The cell wall gene ontology and phytohormone signaling pathway were significantly enriched by DEGs at different periods,indicating that the cell wall gene ontology and the related DEGs on the phytohormone signaling pathway play an important role during pericarp development in the early maturing bud variant material.(4)Early maturation bud transformation may promote ABA synthesis by upregulating NCED1/2 upfront,promote ABA signaling by downregulating the negative regulator PP2 CA,promote ETH and BR signaling by upregulating EBF1 and BRI1,and suppress IAA response factors,genes and receptor expression,which in turn promote PME3/21,LOC102624542,LOC102624542,LOC102613856,EG25,XYL1,LOC102621972,LOC127901308 and PAO expression in the pericarp at fruit ripening,inhibition of CAD and PPO expression,accelerated pectin,cellulose,hemicellulose and chlorophyll degradation,reduced lignin synthesis,and ultimately accelerated fruit ripening softening and color transfer.