Mining for allelic gold: finding genetic variation in photosynthetic traits in crops and wild relatives

Abstract

Improvement of photosynthetic traits in crops to increase yield potential and crop resilience has recently become a major breeding target. Synthetic biology and genetic technologies offer unparalleled opportunities to create new genetics for photosynthetic traits driven by existing fundamental knowledge. However, large “gene bank” collections of germplasm comprising of historical collections of crop species and their relatives offer a wealth of opportunities to find novel allelic variation in the key steps of photosynthesis, to identify new mechanisms and to accelerate genetic progress in crop breeding programs. Here we explore the available genetic resources in food and fibre crops, strategies to selectively target allelic variation in genes underpinning key photosynthetic processes and deployment of this variation via gene editing in modern elite material

Synthetic biology and opportunities within agricultural crops

“…Despite these advancements over the years, crop yields continue to be challenged by the occurrence of pests, weeds, pathogens, nutrient acquisition and abiotic stresses; thus, introducing novel properties and additional genetic diversity is required. However, the ability to overcome these challenges through conventional breeding is limited by the ability to exploit available genetic diversity in crop germplasm collections (Dwivedi et al, 2007, 2017; Sharwood et al, 2022, in press). Genetic and reproductive barriers such as interspecific incompatibility (Bedinger et al, 2011; Kitashiba & Nasrallah, 2014), genetic drag (i.e., introducing unfavourable traits along with any new favourable traits; Langridge & Fleury, 2011; Varshney et al, 2014) and the lack of an effective way to combine multiple desired alleles for complex traits (Lyzenga et al, 2021) remain key limitations for crop breeding programmes to target certain agronomic challenges.…”

“…Enhancing photosynthetic pathways would rely on the SynBio toolkit that can efficiently transfer large gene constructs with specified expression patterns. Examples include enhancing photosynthetic enzymes (Sharwood, 2017; Sharwood et al, 2022) improving WUE by introducing novel aquaporins and modifying cellular anatomy to improve mesophyll conductance (the diffusion of CO 2 into photosynthetic chloroplasts; Cousins et al, 2020; Ermakova et al, 2021). Heat‐shock proteins (Reddy et al, 2016) and altering root traits (Hu & Xiong, 2014) are also targets for improving crop heat and drought tolerance and WUE that should be considered and could be particularly powerful when combined with photosynthetic enhancements.…”

Genetic variation in photosynthesis: many variants make light work

“…Whereas genetic variation in photosynthetic traits is significant in many major crop species (reviewed by Sharwood et al , 2022 and Sakoda et al , 2022 in this issue), incorporation of photosynthesis in selective breeding programmes is still rare. Theeuwen et al (2022) discuss how quantitative genetics can be used to discover useful trait variation and design strategies to improve crop photosynthesis, based on readily available crop plant germplasm.…”

“…Regardless of the mechanism involved, it is clear that expanding allelic diversity can be a fruitful route to enhance breeding programmes. Sharwood et al (2022) review the great potential to find novel allelic variation in photosynthetic traits in large germplasm collections for food and fibre crops and their wild relatives, and how this variation could be leveraged to accelerate genetic progress in crop breeding programmes. Research on Oryza glaberrima (African rice) by Cowling et al (2022) provides a case in point.…”

“…As emphasized by Sharwood et al (2022) , a major challenge still resides in phenotyping of large collections of diverse germplasm, which can quickly become prohibitively expensive. However, methods to enable high-throughput phenotyping for photosynthesis under field conditions have made significant strides driven by advances in sensor technology and statistical techniques, and are starting to make an impact, providing proxies for photosynthetic traits rapidly enough to cover field experiments with several hundred accessions.…”