RiUGT43 transcripts, the RNA readouts used in the study, were about 20 times more abundant in red Rhododendron indicum flowers than in white ones, according to a peer-reviewed analysis of the plant’s UGT genes. The signal also rose with flower-colour depth. That links the transcript level to the colour differences measured here, but does not show that RiUGT43 causes them.
Transient tests in red petals produced a related pattern. In the RiUGT43 overexpression condition, transcript abundance was 20.5-fold higher than in an empty-vector control. Total petal anthocyanin content, measured after acidified ethanol extraction, was 1.48-fold the control, equivalent to a 48% increase. The paper reported both comparisons at P below 0.0001. The result is an association observed in the assay, not evidence of RiUGT43 catalytic activity.
The suppression test showed a smaller change in total anthocyanin content. RiUGT43 transcript abundance was 0.41-fold of the control, while anthocyanin content was 0.88-fold, equivalent to a 12% decrease. Reported thresholds were below 0.0001 for transcripts and below 0.001 for anthocyanin content. The authors therefore limit the interpretation to transcriptional correlation.
A map of the wider gene family
The researchers first built a catalogue of UGT genes in the Rhododendron simsii genome. They compared the genome with 112 Arabidopsis UGT proteins using BLASTP and HMMER, checked candidates for the relevant conserved domain, and removed incomplete sequences. That filtering left 137 sequentially named RsUGT genes. The total is therefore tied to the search and completeness rules used in the study.
A neighbor-joining comparison placed the 137 RsUGT proteins alongside the 112 Arabidopsis reference proteins in 15 subfamilies, labelled A through O. RsUGT43 fell in subfamily E, which had the largest membership. Two further groups, P and Q, were not recovered because matching Arabidopsis reference sequences were unavailable.
Most of the RsUGT genes could be placed on the R. simsii genome map: 126 were anchored to 13 chromosomes, while 11 remained on unanchored genomic sequences. Chr3 carried 21 genes and Chr4 carried 18, compared with one on Chr5. The map shows where the genes are located, but does not by itself establish their biochemical activity.
Expression followed colour and stage
The expression work in R. indicum ‘Huazhui’ used a broader set of comparisons. The researchers identified 48 RiUGT genes and selected 12 for qRT-PCR, examining white, pink and red flowers as well as tissues and stages of red-flower development. The flower-colour transcriptomes used three biological replicates per colour. RiUGT43 expression peaked at full bloom, stage S3, at about 4.8 times the closed-bud stage, S1, and was low in roots, stems and leaves relative to flowers.
In a separate localization test, the researchers attached RiUGT43 to EGFP, a fluorescent tag, and examined the fusion in Nicotiana benthamiana epidermal cells. The signal appeared in both the cytoplasm and nucleus, and an anti-GFP Western blot confirmed that the fusion protein accumulated in infiltrated leaves. This was evidence from a different plant system, not a direct protein measurement in Rhododendron petals.
What the evidence can support
The controls were built into both transient tests. Overexpression used an empty-vector control. The suppression experiment used pTRV1 plus empty pTRV2 as its negative control, while the RiUGT43 construct was paired with pTRV1. For qRT-PCR, technical triplicates were averaged, target expression was normalized against the geometric mean of Actin and EF1α, and the analysis used three biological replicates. Multi-group comparisons used one-way ANOVA followed by Duncan’s multiple range test when ANOVA was significant; two-group comparisons used two-tailed Student’s t-tests.
Even with those controls, the study’s central limitation is that direct RiUGT43 protein accumulation was not demonstrated in Rhododendron petals. The reported anthocyanin differences therefore support a relationship at the transcript level, not an attribution to the protein’s catalytic activity.
Taken together, the study provides a genomic map of the RsUGT family and a transcript-level association between RiUGT43, flower colour and total anthocyanin content in the tested Rhododendron material. Its evidence identifies a pattern to investigate further, while stopping short of showing direct biochemical activity. The research was funded by the Ningbo Innovation Yongjiang 2035 Key Research and Development Program and the Zhejiang Province Bioengineering First-Class Discipline Student Innovation Plan.
Paper data and sources
Original title: Genome-wide analysis of the UGT gene family in Rhododendron and transcriptional correlation of RiUGT43 with anthocyanin accumulation
Authors: Zhong X, Hu G, Jiang Y et al.
Journal/Repository: Frontiers in plant science
Status: Peer-reviewed
First online: 2026-10-08
DOI: Not available
Original paper · Full text