Improved biomass, water use efficiency, and drought tolerance through the simultaneous modification of malate metabolism in guard and vascular companion cells in Nicotiana tabacum

GABRIELA L. MÜLLER; PABLO OITAVEN; GUINDON, MARÍA FERNANDA; VERÓNICA G. MAURINO; DRINCOVICH, MA. FABIANA

Congreso; Translational Research in Crops; 2023

Water limitations pose one of the main challenges for sustainable improvements in crop productivity. Key to such improvements are changes in the efficiency of photosynthesis, the partitioning of assimilates between source and sink organs, and stomatal dynamics. Based on the role of malate in stomatal dynamics and sugar export, we set out to evaluate the impact of modifying malate levels in a compartmentalized manner. We integrated a plastidic NADP-malic enzyme from Zea mays into Nicotiana tabacum using the Potassium channel 1 promoter, which drives expression in guard cells and companion cells of sieve elements. The transgenic plants (TP) show specific morphological characteristics and shorter flowering time than wild type (WT). They also have reduced stomatal aperture under normal and high CO2 growth conditions. The TP show increased net CO2 fixation rate, higher water use efficiency, and higher seed yield. They also export sugars to the phloem at higher rate than WT, likely due to a significant contribution of photosynthesis in cells surrounding the veins to the production of sugars. We propose that the increased sugar export from leaves in the TP alleviates sugar negative feedback on photosynthesis and thus, stomatal closure takes place without a penalty in CO2 assimilation rate. In addition, the TP show tolerance to drought stress. Specially, under severe water stress followed by irrigation, the TP recover and complete the life cycle including seed production, while the WT does not recover. Our results demonstrate that cell type-specific genetic manipulation of malate metabolism can simultaneously increase plant yield and stress tolerance, key traits to designing crops with increased yields under changing climates.