Dissecting heat and drought tolerance in wheat and maize using plant systems biology

Population growth and climate change pose serious threats to food security. Heat and drought are major abiotic constraints to crop production and their co-occurrence will increase during the cropping season in several regions. However, there is a lack of studies investigating their combined effect in crop physiological and biochemical processes. Aiming to close this gap, two of the main crops were investigated, wheat and maize, under these conditions. In the first results chapter, it is shown that these co-occurring stresses equally affect the photosynthetic efficiency of genotypes adapted to Mexico (Sokoll) and the UK (Paragon). However, Paragon recovered faster upon stress relief due to an increased PSII photoprotection and cytosolic Invertase activity, suggesting that optimal sucrose export/utilization and increased electron transport machinery photoprotection are essential to limit wheat yield fluctuations under these conditions. In the second results chapter, by studying maize genotypes with contrasting drought or heat tolerance, it was observed that limited transpiration under high temperature allowed water saving upon deficit without decreasing photosynthetic efficiency. This was sustained by higher phosphorylated PEPC and electron transport rate. Limited transpiration rate and synchronized regulation of the C4 carbon assimilation metabolism showed to be key traits for drought and heat tolerance in maize. In the third results chapter, by screening ten wheat genotypes with different tolerance to drought or heat, it was observed that leaf temperature and evapotranspiration expressed significant genotype-environment interactions. Low leaf number and transpiration efficiency were essential to balance water-saving strategies and biomass production. Changes in the carbohydrate (cytosolic Invertase, Hexokinase, Phosphofructokinase) and antioxidant metabolism (Peroxidases, phenolic compounds) were associated with tolerance mechanisms. Altogether, these results expand our knowledge about crops metabolic responses to high temperature and water deficit. These findings can be further explored in breeding programs to improve crop resilience to climate change and meet food security