Using genetic variation in chilling-induced photoinhibition to enhance cold tolerance in maize.

The C4 crop maize is a global food, feedstock and bioenergy 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 efficiencies 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. 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 inactivation of the photosynthetic apparatus. 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.

This project aims to improve chilling tolerance in maize. We have previously developed detailed knowledge of how variation at specific genomic locations between contrasting maize lines is correlated with chilling tolerance. In addition, we identified transcriptional networks controlling tolerance to chilling and developed novel tools to assess gene transcription responses to chilling stress across two important leaf tissue types. We now aim to use this scientific progress to both increase our fundamental understanding of maize chilling tolerance, as well as enhance the applicability of our previous findings in maize breeding programs. To do so, crosses between maize lines carrying contrasting haplotypes for the most promising QTL will be used to study the mode of action (dominant, recessive, etc). In addition, sensitive and tolerant maize lines will be crossed to a common tester line to evaluate the gene regulatory networks in response to chilling stress in a hybrid background. Finally, gene regulatory networks in response to chilling will be studied in the two contrasting photosynthetic cell types in maize, bundle sheath cells and mesophyll cells, using newly developed maize lines that allow specific analysis of gene transcript abundance in these cell types.