Adaptations to low temperatures in C4 grasses

Low temperatures significantly impact plant survival, particularly for species unable to acclimate to such conditions. Grasses, including those with C3 photosynthesis, have shown remarkable resilience across broad temperature ranges, particularly in temperate and high-altitude regions with low mean annual temperatures. Although C4 grasses typically originate from warmer climates, some can adapt to and thrive in colder environments. Given the importance of C4 grasses like maize, sugarcane, and sorghum as food sources, understanding how C4 grasses respond and adapt to low temperatures is crucial for future food security. While existing research has shed light on how certain C4 grass species respond to cold, comprehensive studies across diverse lineages are limited. Our study aims to fill this gap by investigating how various C4 grasses respond to and adapt to low temperatures, focusing on leaf anatomy, transcriptomics, and physiological responses.

In our leaf anatomy analysis, we observed interspecific adaptations in temperate grasses, characterised by small mesophyll area and reduced metaxylem cell size, as potential keys to maintaining photosynthetic efficiency and water transport under cold conditions. However, intraspecific leaf adaptations in Alloteropsis semialata revealed unique patterns, with genotypes from cooler regions developing large phloem areas, potentially aiding in sugar translocation under low temperatures. Transcriptomic comparisons between C3 temperate and C4 tropical species revealed shared and distinct gene expressions in response to cold, indicating potential common and unique adaptations among grass lineages. Finally, physiological experiments with A. semialata highlighted common photoprotective mechanisms across genotypes, regardless of their photosynthetic pathways or geographic origins. Our findings suggest that the photosynthetic type, rather than geographic origin, plays a significant role in determining the tolerance of grass species to low temperatures in high-light environments.

In conclusion, our study investigates various adaptations in C4 grasses to cold climates. We found unique and consistent leaf anatomical adaptations among C4 temperate grasses and observed shared and distinct gene expressions between C3 and C4 species. Our findings highlight the importance of photosynthetic type and geographic origin in determining how grasses tolerate low temperatures.