Photosynthetic response to genome methylation affects the growth of Chinese white poplar

Genome methylation plays a key role in regulating gene expression, but limited knowledge exists concerning the link between DNA methylation and economic traits in forest trees. We measured photosynthetic characteristics and growth traits in 130 intraspecific hybrids of Chinese white poplar (Populus tomentosa Carr.) and detected their genome methylation. The phenotypic data were normally distributed, and each trait had a significant difference among the hybrids. The net photosynthetic rate (Pn, 14.83 ± 3.76 μmol m⁻² s⁻¹), stomatal conductance (Gs, 0.29 ± 0.09 mol m⁻² s⁻¹), and intercellular CO₂ concentration (Ci, 264.50 ± 30.94 μmol mol⁻¹) showed similar trends. Positive correlations were found between Pn and height (H, 133.59 ± 50.44 cm) and basal diameter (D, 16.29 ± 5.20 mm), respectively. Using methylation-sensitive amplification polymorphism (MSAP) analysis, 32 primer-pair combinations generated 715 polymorphic markers. Positive correlations between photosynthetic characteristics, such as Pn and Gs, and total relative methylation level and relative hemimethylation (CNG methylation) level were investigated. Eighty-one candidate markers were associated with Pn, Gs, or Ci, 13 of which were also associated with growth traits using single MSAP molecular marker association. Sequencing and BLAST analysis showed that candidate markers were linked to genes encoding protochlorophyllide reductase and proteins of cytochrome P450 CYP4/CYP19/CYP26 subfamilies, and linked to genes taking part in, e.g., photosystem II. Therefore, the regions defined by the MSAP candidate markers are linked to genes that are essential for photosynthetic characteristics that respond to DNA methylation and subsequently affect growth traits.