PagPIP1;2 overexpression increases leaf CO2 conductance, photosynthesis, and biomass accumulation in poplar

Forests produce wood biomass and remove atmospheric carbon dioxide (CO 2 ) via photosynthesis. Mesophyll conductance ( g m ) is a major limiting factor in leaf photosynthesis. Improving g m in leaves by modulating plasma membrane intrinsic proteins (PIPs) could be a new approach for enhancing photosynthesis and biomass accumulation in trees. In this study, the effects of overexpressing PagPIP1;2 , which is an NtAQP1 -like gene, on the leaf anatomical structure, mesophyll conductance, and photosynthetic characteristics of poplar seedlings were investigated. PagPIP1;2 overexpression (OE) lines exhibited substantial increases in whole-plant biomass (58%–136%) and net photosynthetic rate (42%–51%). Moreover, stomatal conductance ( g s , 27%–69%), photosynthesis-based g m (43%–77%), Rubisco activity, maximum carboxylation rate, and photosynthetic nitrogen use efficiency were significantly improved, whereas leaf water use efficiency remained unchanged. The components of g m were further analyzed using ultra-anatomical data of the leaf. Chloroplast ( g st ) and cell wall ( g cw ) conductance were significantly increased, thereby promoting liquid phase conductance ( g liq ) in OE lines. Anatomical features, such as increased mesophyll surface area and chloroplasts facing the intercellular space per unit leaf area, could increase g st and g cw , thereby boosting anatomy-based g m , particularly in the palisade tissue. Limitations of CO 2 transport in the mesophyll were alleviated. The Rubisco activity and photosynthetic biochemical parameters were also increased. Overall, these results suggest that PagPIP1;2 can enhance leaf g s , g m , and biochemical capacity, which significantly promote leaf photosynthesis and whole-plant biomass assimilation in 84 K poplar. • Leaf photosynthesis and g m of PagPIP1;2 overexpression lines were investigated. • P n and biomass accumulation were significantly increased in OE lines. • Increased g st and g cyt could be the main contributors to leaf g m . • Palisade and spongy cells responded differently to PagPIP1;2 overexpression.