Allelic variation in PtoPsbW associated with photosynthesis, growth, and wood properties in Populus tomentosa.

Photosynthesis is one of the most important reactions on earth. PsbW, a nuclear-encoded subunit of photosystem II (PSII), stabilizes PSII structure and plays an important role in photosynthesis. Here, we used candidate gene-based linkage disequilibrium (LD) mapping to detect significant associations between allelic variations of PtoPsbW and traits related to photosynthesis, growth, and wood properties in Populus tomentosa. PtoPsbW showed the highest expression in leaves and it increased during the development of these leaves, suggesting that PtoPsbW may play an important role in plant growth and development. Analysis of nucleotide diversity and LD revealed that PtoPsbW has low single-nucleotide polymorphism (SNP) diversity (π tot = 0.0048 and θ w = 0.0050) and relatively low average value of LD (0.1500), indicating that PtoPsbW is conserved due to its indispensable function. Using single-SNP associations in an association population of 435 individuals, we identified five significant associations at the threshold of P ≤ 0.05, explaining 3.28-15.98 % of the phenotypic variation. Haplotype-based association analyses indicated that 13 haplotypes (P ≤ 0.05) from six blocks were associated with photosynthesis, growth, and wood properties. Our work shows that identifying allelic variation and LD can help to decipher the genetic basis of photosynthesis and could potentially be applied for molecular marker-assisted selection in Populus.