LIFE: Tracing the origins of (biochemical) breakthroughs promoting repeated chilling tolerance evolution in warm-season grasses

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

The goal of this project is to characterize the developmental, physiological, biochemical, and transcriptional mechanisms that underlie chilling tolerance in some grasses, and to use this information to improve the thermal tolerance of specific cereal crops. Cold temperatures in the US cause millions of dollars of damage to crops every year. This is particularly true for crops domesticated from tropical species, such as the grass cereals corn, sorghum, and millet. One reason that tropics-derived cereals fare best in warm environments is their special type of photosynthesis known as “C4". Photosynthesis is the process by which CO2 is converted into sugars, and it requires the diffusion of air through open pores, such that plants lose water when conditions are dry/hot. C4 cereals and their relatives have repeatedly evolved a trick whereby CO2 is concentrated in cells, allowing their pores to close and conserve water without greatly reducing photosynthetic sugar production. This strategy works well when temperatures are high, but it comes at the cost of poor tolerance to colder temperatures or "chilling tolerance". The aim of this project is to better understand how some C4 grasses have been able to circumvent the tradeoff between C4 photosynthesis and cold tolerance with an eye to designing C4 cereals that thrive under a range of temperatures. The first step is to determine the number of origins of chilling tolerance in the hundreds of C4 cereal grasses, and then to determine how chilling-tolerant C4 grasses are physiologically and genetically distinct from their chilling-sensitive counterparts. Finally, C4 enzymes will be strategically targeted for modification in corn and millet with the aim of increasing the chilling tolerance of these species. Beyond the goal of translating this research into designing chilling-tolerant crops to improve US agriculture, this project will provide excellent training opportunities to post-doctoral fellows, undergraduate and graduate students and will generate rich resources for the broader scientific community. Complex traits have evolved repeatedly across all domains of life, but it is still something of a mystery as to how this can occur. This proposal seeks to explore the mechanisms underlying convergent trait evolution by focusing on independent origins of chilling tolerance in the C4 grass clade Panicoideae: Paniceae, containing maize, sorghum, and millets among its roughly 1,500 members. The first objective is to characterize an integrated measure of chilling tolerance across the subfamily, reconstruct its number of origins, and determine the degree to which different developmental, physiological, biochemical, and transcriptional responses to cold correlate with its independent origins. The second objective is to focus specifically on the evolution and biochemistry of typically cold-sensitive enzymes of the C4 photosynthesis pathway where increased abundance and/or activity below 15 C have been implicated in more chilling-tolerant plants. The third objective is to select a subset of chilling-tolerant enzymes to express in corn and Setaria viridis to test for modifications towards chilling tolerance at the whole plant level. Beyond answering questions about how convergent traits can evolve, expected outcomes of the project are a better understanding of the magnitude of changes required to engineer chilling tolerance, the number of evolutionary paths that have been taken to this trait, and specific paths to increased chilling tolerance in corn and its relatives. This award is co-funded by the BIO-IOS-Physiological Mechanisms and Biomechanics (PMB) program and the BIO-DEB-Systematic and Biodiversity Science (SBS) program. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.