Transcriptome and Metabolome Analyses Provide Insights into the Occurrence of Peel Roughing Disorder on Satsuma Mandarin (Citrus unshiu Marc.) Fruit

Abstract

Roughing disorder (RD) is a significant quality barrier in citrus fruit, prevalent on easy-peeling mandarins. As RD is not yet well-understood, this study aimed to examine the changes and synergic molecular processes involved in peel RD. Peel with RD was induced by severely defruiting Satsuma mandarin trees. Morphology observations, RNA-sequencing, and targeted and untargeted metabolic analyses were conducted. The results showed that the primary metabolites of sugars, organic acids and amino acids are dramatically changed in RD peel. The RD peel was always characterized by higher magnesium content during development. Comparative transcriptome profiling was performed for CK and RD peels at 30, 80, and 170 days after full bloom (DAFB) which represented fruit at cell division stage, cell enlargement stage and fruit maturity stage, respectively. Physiological and molecular biological evidence suggested that the month after full bloom is a crucial stage for RD initiation. A total of 4,855 differentially expressed genes (DEGs) in RD peel, relative to CK peel were detected at cell division stage, about 2 to 4-fold more than other stages had. Among the differentially expressed transcription factors, the bHLH family were affected most by RD, and six bHLH transcription factors functionally involved in GA metabolism were assessed to associate with RD occurrence. Gene set enrichment analysis suggested that RD significantly altered starch and GA metabolism in peel. Higher starch content and hydrolysed chain status were found in RD peel at cell division stage. RD occurrence on the peel was influenced significantly by GA, especially abundant GA before July. These changes may mean a significant alteration in sink strength of RD peel. The findings of this study provide insights into the emergence, development and molecular mechanisms of RD.

Transcriptome and Metabolome Comparison of Smooth and Rough Citrus limon L. Peels Grown on Same Trees and Harvested in Different Seasons

“…Of the other key differences, changes in cell wall composition seemed to be dominant since, in almost all of the treatment comparisons (except C5 vs. D4 in transcriptome), we observed the differential regulation of related genes and accumulation of related metabolites (Supplementary Tables 3-5). This observation is consistent with a previous study on the differential accumulation of cell wall-related metabolites and changes in cell wall thickness in mandarins (Lu et al, 2017). In this regard, the exclusive expression of XTH22 and XTH24 is quite relevant to the visible phenotype of D, i.e., thicker peel (Supplementary Tables 3, 5).…”

“…The authors reported that sugars, organic acids, and amino acids and derivatives were the main metabolites that were differentially accumulated. Particularly, the amino acids and derivatives accumulated in higher quantities in the RD peels (Food and Agriculture Organization, 2017;Lu et al, 2017). The authors of a latest study only considered the peels of fruits at 170 days after full bloom, thus, leaving a knowledge gap between the early developmental stages of the citrus peels (Lu et al, 2017).…”

“…Particularly, the amino acids and derivatives accumulated in higher quantities in the RD peels (Food and Agriculture Organization, 2017;Lu et al, 2017). The authors of a latest study only considered the peels of fruits at 170 days after full bloom, thus, leaving a knowledge gap between the early developmental stages of the citrus peels (Lu et al, 2017). Another study on the development of citrus peels has reported the differential accumulation of organic acids and derivatives, polyphenols, amino acids and derivatives, flavones, and nucleotides and derivatives (Wang et al, 2020).…”

The involvement of PybZIPa in light-induced anthocyanin accumulation via the activation of PyUFGT through binding to tandem G-boxes in its promoter

“…More recently, multiomics integration analysis has been applied to study plant development 27–29 , environmental responses 30–33 , and other biological processes 34–36 . Specifically, transcript and metabolite datasets have been analyzed and compared, integrated through correlation and cluster analyses and ultimately used to reveal the relationships between genes and metabolites in Arabidopsis 30,35,37,38 and fruit trees such as citrus 29,32,39 , grape 40,41 , kiwifruit 42 , lichi 43 and fig fruit 44 trees. Integrated analysis of “omics” datasets (i.e., transcriptome and metabolome) can provide an effective strategy for identifying potential genes regulating light-induced anthocyanin biosynthesis in red Chinese sand pear.…”

APPLICATION OF K, Ca, and Mg ON PEEL THICKNESS AND FRUIT CRACKING INCIDENCE OF CITRUS

“…The development of fruit skin thickness in the two varieties is in accordance with the phase of growth and development which is differently intervals for each variety. According to Lu et al (2017), in Satsuma Mandarin the development of fruit is characterized by the increase of diameter size along with the thickening of fruit skin until the age of 30 days. Then with increasing age, the size of the fruit increases but the thickness of the skin decreases until the ripening phase.…”