RNA sequencing links radial fiber traits to gene activity in two eucalypts

A comparative study of six-year-old eucalypt clones found that two commercially important types differed consistently in wood-fiber anatomy but showed different patterns of gene activity across the trunk. In all four radial zones examined, Eucalyptus cloeziana had significantly greater fiber double-wall thickness, while the Eucalyptus urophylla × E. grandis hybrid had greater fiber lumen width. Measurements of both traits varied less among the four zones in the hybrid. The study also found that adjacent zones in the hybrid contained more than twice as many differentially expressed genes as adjacent zones in E. cloeziana, indicating that comparatively stable fiber traits coincided with extensive transcriptional change.

The researchers examined clones of both eucalypt types, measuring fiber double-wall thickness and fiber lumen width across four radial zones: the outer trunk phloem, outer sapwood, inner sapwood and transition zone. The anatomical patterns were clear. E. cloeziana had thicker fiber double walls throughout the sampled sequence, whereas the hybrid had wider fiber lumens in every zone. Despite those consistent differences between the two eucalypt types, the hybrid showed less radial variation in both measurements. Because the analysis involved one age and one comparison of clones, the results characterize the sampled developmental stage rather than establishing how the differences develop over a tree’s lifetime.

To investigate the molecular basis of the anatomical contrasts, the team performed comparative RNA-sequencing analyses on tissue from the four radial zones. The transcriptome did not mirror the relative stability of the measured fiber traits. Although the hybrid’s double-wall thickness and lumen width changed relatively little among zones, gene-expression differences between neighboring zones were substantially more numerous than in E. cloeziana. The authors interpret this contrast as evidence for a dynamic transcriptional network that may buffer phenotypic variation during radial growth in the hybrid. That is a mechanistic interpretation supported by the expression and trait data, rather than direct proof that individual expression changes cause the observed stability.

Functional enrichment analysis of the differentially expressed genes predominantly identified pathways associated with the biosynthesis of other secondary metabolites and phenylpropanoid biosynthesis. The researchers proposed that coordinated activity in these pathways may reflect the allocation of carbon and lignin deposition associated with wood formation in the hybrid. This places the transcriptional response in a metabolic context linked to the construction of secondary cell walls, although the comparative analysis does not establish the direction of causation between expression changes, lignin deposition and fiber anatomy. It also does not show that the abundance of differentially expressed genes alone determines radial growth.

The study additionally identified gene modules that were significantly associated with fiber double-wall thickness and fiber lumen width. These associations highlighted candidate genes involved in regulating cell-wall thickness in eucalypts and narrowed the set of genes that may be relevant to the measured wood traits. Module membership and trait association do not, however, demonstrate the function of any individual gene in controlling cell-wall formation. The authors describe the results as a foundation for understanding regulatory mechanisms of radial growth in hardwoods and as a theoretical basis for genetic improvement of Eucalyptus wood properties. Overall, the evidence supports three linked findings: distinct radial fiber anatomy in the two eucalypt types, greater phenotypic stability of two fiber traits in the hybrid, and correspondingly dynamic gene expression associated with secondary-metabolite and phenylpropanoid pathways.

Subject of Research: Comparative transcriptomics of radial wood-fiber trait variation in two Eucalyptus types.

Article Title: Comparative transcriptomic analysis of radial growth regulation in Eucalyptus urophylla × E. grandis and E. cloeziana

Article References: Wang, X., Lei, D., Li, M., Pan, M., Cen, H., Xu, Z.-F., & Li, K. (2026). Comparative transcriptomic analysis of radial growth regulation in Eucalyptus urophylla × E. grandis and E. cloeziana. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10193-6

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10193-6

Keywords: Eucalyptus, radial growth, wood formation, RNA sequencing, fiber cell walls, differential gene expression, phenylpropanoid biosynthesis, lignin deposition, comparative transcriptomics, Comparative, transcriptomic, analysis