Understanding the molecular regulation of citric acid accumulation in citrus fruits is crucial, as acidity directly influences fruit flavor, consumer preference, and commercial value. Citric acid is the predominant organic acid in citrus, and its levels are shaped by several factors, including genetic and developmental factors. ‘Jinyan’ Bingtang orange (Citrus sinensis cv. Jinyan) is a novel mutant derived from ‘Jinhong’ Bingtang orange (C. sinensis cv. Jinhong) that has a noticeably sour taste. However, the molecular basis of the increased citrate content in ‘Jinyan’ fruits remains unclear. This study compared the organic acid profiles and expression of citric acid metabolism-related genes between ‘Jinyan’ and ‘Jinhong’ fruit juice sacs throughout fruit development. The trend of citric acid content in both cultivars was similar; however, ‘Jinyan’ consistently presented significantly higher levels than ‘Jinhong’ did from 95 to 215 days after flowering (DAF). After 155 DAF, the transcript levels of citrate biosynthesis-related genes (PEPC1, PEPC2, PEPC3, CS1, and CS2) and citrate transport-related genes (V₁-E1, V₁-E2, V₀-a2, V₀-d, VHP1, VHP2, and CsPH8) were significantly greater in ‘Jinyan’ than in ‘Jinhong’. In contrast, citrate degradation-related genes (NAD-IDH2 and NAD-IDH3) were expressed at lower levels than in ‘Jinhong’. Notably, the expression patterns of V₁-E2 and CsPH8 closely matched the changes in citrate content in both cultivars. These results indicate that, compared with ‘Jinhong’, high citric acid accumulation in the juice sacs of ‘Jinyan’ fruit is likely due to increased citrate synthesis (via upregulated PEPCs and CSs) and increased vacuolar citrate sequestration (via upregulated proton pumps and transporters), coupled with reduced citrate degradation (lower NAD-IDH2/3).

Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is commonly managed with copper-based formulations, yet the performance of individual products may differ between laboratory and plant assays. We compared 16 commercial copper-containing formulations in plate-diffusion and root-drench assays, and inhibition zones varied among products. Thiosen Copper, however, produced no visible inhibition zone on agar but suppressed Xcc growth after root application. In sweet orange, this suppression appeared earlier than with Bordeaux Mixture at the same nominal total Cu concentrations. Thiosen Copper raised the leaf chlorophyll index without a significant increase in total leaf Cu, whereas Bordeaux Mixture led to greater leaf Cu accumulation. In separate experiments with Poncirus trifoliata, the two formulations produced different growth and tissue Cu responses, and root treatment altered PtCOPT transcript levels. Transient overexpression of CsCOPT4 in sweet orange leaves was accompanied by lower Xcc populations. These results reveal formulation-specific responses and nominate CsCOPT4 as a candidate for further study.

Plant GATA transcription factors are zinc-finger proteins involved in signal transduction, growth and development. However, their potential involvement in plant height and gibberellin-associated shoot growth in pummelo insufficiently characterised. In this study, members of the CgGATA gene family were identified genome-wide and characterised through analyses of physicochemical properties, chromosomal distribution, phylogenetic relationships, gene structures, conserved motifs, collinearity and predicted cis-acting elements in putative upstream regulatory regions. RT-qPCR was used to examine expression profiles across sampled tissues, and expression changes associated with prolonged gibberellin (GA₃) treatment in ‘Wanbai Pummelo’ shoot tips, and expression patterns in tall and dwarf pummelo genotypes. A total of 23 CgGATA genes were identified and classified into four phylogenetic subfamilies. Members of the same subfamily generally shared similar gene structures and conserved-motif compositions. Comparative collinearity analysis identified more syntenic GATA gene pairs between pummelo and sweet orange than between pummelo and Arabidopsis thaliana. The putative upstream regulatory regions contained predicted elements associated with light, phytohormone, growth and stress responses. The genes exhibited distinct expression profiles across the sampled tissues, with many showing relatively high within-gene values in stems and leaves. Prolonged GA₃ treatment promoted seedling shoot elongation and was associated with changes in the transcript abundance of several CgGATA genes at 28 d. Integration of these expression profiles, the tall dwarf comparison and predicted gibberellin-responsive elements prioritised CgGATA11 and CgGATA18 as candidates for investigating plant height variation and shoot elongation in pummelo. These findings provide a basis for functional studies but do not establish that either gene directly regulates gibberellin signalling or plant height.