Does maize suffer from cold feet?

Maize is an important global food, feedstock and bioenergy crop. In the UK, maize is an increasingly popular crop for animal fodder and for use in anaerobic digesters to provide bioenergy, reflected in an acreage increase of 19% between 2017-2022. Maize was domesticated by ancient farmers in Mexico approximately 9000 years ago and is one of the most susceptible crops to chilling stress 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. Chilling stress in maize is most common at the start of the growing season, where it leads to poor establishment, which decreases maize ability to efficiently capture light, compete with weeds and take up nitrogen fertilizer. In addition, chilling stress decreases general plant health and enhances susceptibility to plant pathogens. While later planting dates would decrease the prevalence of chilling stress, sustainable farm management increasingly focuses on early harvest (which necessitates early sowing) to allow sufficient growing time for cover crops at the season’s end to minimize nitrogen leaching. Altogether, understanding maize chilling stress is clearly important for improving yield security and sustainability of maize cultivation. However, despite decades of research efforts, a full mechanistic understanding of chilling sensitivity in maize is still lacking. Here, we postulate that maize chilling sensitivity under field conditions results from two distinct responses. In addition to whole-plant chilling stress, which is well-studied, we propose that root-shoot temperature gradients lead to additional, potentially confounding, stress symptoms. Due to the high specific heat capacity of soil compared to leaves and surrounding air, roots respond much slower to changes in temperature. As a result, root-shoot temperature gradients are commonplace during regular diurnal cycles, as well as during chilling episodes. We recently found that root-specific chilling already creates significant damage and downregulation of photosynthesis at mild chilling temperatures at which plants can safely tolerate whole-plant chilling. These results suggest that chilling stress symptoms under field conditions could reflect both maize’ poor capacity to cope with low temperature per se, as well as with cool temperature of roots relative to shoots. This project will deconvolute the impact and underlying mechanisms of whole plant chilling and root-specific chilling using an experimental set up in which root and shoot temperature are separately controlled. Using this set up, the proposal aims to define temperature thresholds for damage and plant survival under root-chilling and whole-plant chilling treatments and corresponding root and shoot transcriptomic profiles. The work also aims to determine the role of root versus shoot synthesis of the plant hormone abscisic acid (ABA), which is involved in maize chilling responses as well as root-shoot communication. Finally, the project will analyse the mechanism underpinning downregulation of photosynthesis as a result of whole-plant-chilling and root-chilling stress, using a novel genetic mutant line impaired in photoprotection. The project outcomes will enhance our understanding of maize chilling stress under field conditions, which is important for delivering the vision set out in the BBSRC Research in Agriculture and Food Security Strategic Framework, in particular for focus areas ‘Sustainable Agricultural Systems'.