Effects of environmental conditions before gene transfer on the amount of influenza hemagglutinin transiently expressed in Nicotiana benthamiana leaves

Abstract

　We investigated the effects of photosynthetic photon flux density (PPFD), air temperature, and CO₂ concentration before gene transfer on the accumulation level of hemagglutinin (HA), an influenza vaccine antigen, in Nicotiana benthamiana leaves in a transient gene expression system. Plants were treated for two weeks before gene transfer with different levels of PPFD, air temperature or CO₂ concentration in separate experiments. Leaf fresh mass (FM), leaf HA content per unit FM, and leaf HA content per plant at 6 d post infiltration (6 DPI) for gene transfer all tended to increase with increasing average PPFD during the treatment period. Leaf FM and leaf HA content per plant at 6 DPI were significantly greater at an average day air temperature of 25°C-30°C during the treatment period than at 20°C-25°C. No clear effects of CO₂ concentration were found on either growth or leaf HA content under the conditions tested in the present study. There was a positive correlation between leaf HA content per unit FM at 6 DPI and leaf FM at 0 or 6 DPI in plants grown under different PPFDs and air temperatures. Preparing plants with increased leaf FM by applying high PPFD and/or high air temperature before gene transfer should increase not only total HA yield per plant but also HA content per unit leaf biomass at harvest.