Abstract
Xyloglucan endo-transglycosylases (XETs) modify the xyloglucan-cellulose framework of plant cell walls and, thus, affect cell wall expansion and strength. Dissecting the mechanism by which natural variation in XETs affects wood properties can inform breeding efforts to improve wood quality and yield traits. To this end, we isolated a full-length PtoXET16A cDNA clone from Populus tomentosa. Real-time PCR analysis showed that PtoXET16A was maximally expressed in the root, followed by phloem, cambium, and developing xylem, suggesting that PtoXET16A plays important roles in the development of vascular tissues. Nucleotide diversity and linkage disequilibrium analysis revealed that PtoXET16A has high single nucleotide polymorphism (SNP) diversity (π = 0.01266 and θw = 0.01392) and low linkage disequilibrium (r2 ≥ 0.1, within 900 bp). SNP- and haplotype-based association analyses of 426 individuals from a natural population indicated that nine SNPs (including two non-synonymous markers and one splicing variant) (p ≤ 0.05, false discovery rate Q ≤ 0.01), and nine haplotypes (p ≤ 0.05) were significantly associated with growth and wood properties, each explaining from 3.40%–10.95% of phenotypic variance. This work shows that examination of allelic variation and linkage disequilibrium by a candidate-gene-based approach can help to decipher the genetic basis of wood formation. Moreover, the SNP markers identified in this study can potentially be applied for marker-assisted selection to improve growth and wood-property traits in Populus.
Highlights
Woody tissues are composed of various biopolymers and provide an enormous, renewable feedstock for pulp and paper, biofuels, and solid wood products [1]
A full-length cDNA encoding a XET16A-like protein was isolated from a cDNA library prepared from mature xylem zone of P. tomentosa
We found that the strongest relative expression of PtoXET16A
Summary
Woody tissues are composed of various biopolymers and provide an enormous, renewable feedstock for pulp and paper, biofuels, and solid wood products [1]. Forest tree-breeding programs aim to improve the quantity and quality of wood products from trees grown in plantations. Considering that small improvements in quantitative traits may deliver large gains, identification of genes and gene variants controlling growth and wood quality traits can provide important information for forest tree-breeding programs. Xyloglucan endo-transglycosylases (XETs), among the most important enzymes affecting cell wall expansion and strength, modify the xyloglucan-cellulose framework of plant cell walls [2]. The XETs make up part of a multigene family of xyloglucan endo-transglycosylases/hydrolases (XTHs) [5]. Previous studies showed there are 33 XTH members in Arabidopsis thaliana [7], 29 in rice (Oryza sativa) [8]
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