KNAT7 transcription factor regulates metabolite and ion profiles to control cell wall biosynthesis in Populus

Poplar (Populus spp.) is widely recognized as a fast-growing woody species with considerable potential for sustainable bioenergy production, largely due to the high cellulose content of its secondary cell walls. Members of the KNOTTED1-like homeobox transcription factor family are known regulators of plant development, and KNAT7 has been closely associated with secondary wall formation and lignification. In the present study, metabolite and ion profiles were examined in transgenic poplar lines with KNAT7 overexpression and antisense suppression to elucidate its role in metabolic regulation during wood formation. Pronounced alterations in primary metabolism were observed in KNAT7-overexpressing lines, including substantial increases in soluble sugars such as glucose, gluconic acid, mannitol, sucrose, xylitol, and cellobiose, indicating enhanced carbon allocation toward cell wall polysaccharide biosynthesis. Amino acid metabolism was also significantly affected, with elevated levels of L-glutamic acid and L-5-oxoproline, as well as increased abundance of phenylalanine and tyrosine, key precursors of the lignin biosynthetic pathway. In addition, several phenolic and defense-related secondary metabolites, including hydroquinone, resveratrol, salicylic acid, and 4-hydroxybenzoic acid, were enriched, suggesting coordinated regulation of structural reinforcement and stress responsiveness. Elemental profiling revealed increased accumulation of Na, Mg, Fe, Mn, Zn, and Cu, with magnesium showing notable enrichment, consistent with its role as a cofactor in enzymes associated with lignin biosynthesis. Overall, the findings indicate that KNAT7 modulates metabolite and ion homeostasis in support of secondary cell wall biosynthesis, underscoring its potential utility for genetic improvement of wood quality and bioenergy-related traits in poplar.