Compartmentalized expression of maize non photosynthetic NADP-ME resulted in improved plant productivity in normal and drought stress conditions

GUINDON, MARÍA FERNANDA; SAPER, CAROLINA; OITAVEN, PABLO; SREBOT, MARÍA SOL; MÜLLER, GABRIELA L.; DRINCOVICH, MA. FABIANA

Congreso; Reunión anual Edición LVIII; 2022

NADP-malic enzyme (NADP-ME) has been suggested to play important roles in diverse stress responses in plants. Nicotiana tabacum transgenic plants expressing maize non photosynthetic NADP-ME (npNADP-ME) under the KAT1 promoter resulted in enhanced water use efficiency, earlier flowering and shorter life cycle under normal conditions. Also, these lines exhibit reduced stomatal aperture, increased sugar export from leaves and increased net CO2 fixation rate compared to WT possibly due to npNADP-ME activity in guard and companion cells driven by the KAT1 promoter. To better understand the phenotype of these plants we studied them under normal and drought stress growing conditions. Under normal conditions, quantitative real-time PCR was performed, showing that npNADP-ME was expressed at stem and leaves of transgenic lines; but it was undetectable in roots and seeds, while it was not observed in any tissue of WT plants. In order to investigate the performance of these plants under drought conditions, plants were grown for 60 days and then irrigation was stopped for 30 or 45 days. Finally, plants were irrigated until the end of the cycle and total dry stems, leaves and fruits were collected. Three plants of each line were evaluated for each treatment. WT plants were not able to recover after the 45 days of drought. In all the other conditions, the harvest index, calculated as the ratio between seed yield and dry biomass, was higher in transgenic plants (at least 2 fold), with an average value of 0.41 in control conditions and 0.43 after 30 days of drought versus 0.15 and 0.20 values for WT. Average number of seeds per fruit and number of seeds per plants were also greater in the transgenic lines, either in control conditions (61224.12 and 2514.54 vs 25800.73 and 1245.84) or after 30 days of drought 42579.34 and 2146.38 vs 24612.13 and 1174.46). These lines produce a larger number of smaller seeds. 1000-seed weight decreased compared to WT in both treatments (0.05 and 0.06 vs 0.08 and 0.08) but there is no significant difference among the genotypes in the proportion of protein or glucose content. Considering all, the overall effect in yield is an increase between 1.4 to 1.8-fold in the rams of seed per plant of the transgenic lines in comparison to the WT. Leaf relative water content (RWC) was also followed. In control conditions, RWC was similar in transgenic and WT plants. During drought stress, the RWC declined in the same proportion for all the genotypes (34-41%). Xylem vessels diameter in control conditions were characterized using light microscopy evidencing differences between genotypes. The results demonstrated that modification of the levels of NADP-ME in the guard and vascular companion cells of tobacco is a promising approach for the improvement of plant productivity, especially in drought conditions.