TRANSCRIPTIONAL REGULATION OF RESILIENCE TO PHOTO-INHIBITION UNDER CHILLING CONDITIONS IN MAIZE.

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Global food demand is expected to increase substantially over the coming decades, with a predicted increase in human population from 7.5 billion currently to 10 billion by 2050 and significant shifts to increasingly calorie-rich diets. This comes at a time when productivity increases of several major food crops through conventional breeding have slowed down and global climate change is putting additional pressures on food production, especially via extreme weather events. Investing in sustainable and resilient crop productivity per unit land area is urgently needed, if humanity is to successfully avert future global food crises.The C4 crop Zea mays (maize) is currently the dominant global crop with a world-wide production volume of 1.09 billion metric tons. Crop species with the C4 photosynthetic pathway circumvent some of the inefficiencies of the Calvin-Benson-Bassham cycle by concentrating carbon dioxide around its central enzyme Rubisco. The physiological advantages of C4 species, such as high efficiency of photosynthetic light, water and nitrogen use, have allowed several of these species to become agriculturally relevant crops or weeds, and to dominate many of the open landscape biomes across warmer regions of the earth. They also form the rationale for attempts to improve productivity of C3 crops such as rice, by installing C4 biochemistry and anatomy.However, crops originating from the tropics and sub-tropics are often sensitive to chilling temperatures, in particular in combination with exposure to light which gives rise to chilling-induced photoinhibition, i.e. prolonged periods where plants are incapable of doing photosynthesis and are very sensitive to damage by absorbed sunlight. Maize was domesticated by ancient farmers in Mexico approximately 9000 years ago and is one of the most susceptible crops to chilling-induced photoinhibition amongst those grown in temperate regions. As a result, maize yields at higher latitudes are limited by a relatively short growing season and maize is sensitive to yield losses due to early and late season cold snaps and poor early season establishment of sufficient leaf area to efficiently capture light and compete with weeds.Improving chilling tolerance in maize will have strong economic impact by increasing the latitudinal range of maize and by helping to reduce year by year yield variability. It has been known for a long time that considerable variability in chilling tolerance and photoinhibition sensitivity exists amongst different maize accessions, often reflecting the climate at the region of cultivar development, such as between dent varieties from the US corn belt and flint varieties developed in more temperate regions like Northwest Europe, Canada or Argentina, but the mechanistic and genetic basis of this variation still remains largely undefined. The central aim of this project is to improve understanding of genetic differences in sensitivity to chilling-induced photoinhibition to aid development of superior maize germplasm for temperate regions.This project will use a novel maize population with structured genetic variation to identify differences in traits involved in chilling-induced photoinhibition that are statistically correlated to genetic variation. Similarly, variation in gene expression levels will be measured and correlated to sequence variation at specific genomic locations. Using these parallel experimental approaches under field and controlled environment conditions, the project will identify specific genes that are central in controlling gene expression in response to chilling and high light, as well as pinpoint which genomic locations in maize show variation that correlates with the expression of these control genes. The projects outcomes will increase availability of genetic markers for breeding of chilling-tolerant traits, as well as enhance understanding of the role of gene expression responses in improving chilling-tolerance in maize.