Overview
Food security is a primary concern of mine. Roughly 1-in-8 people are classified as mal-nourished or undernourished today, global population continues to rise, and the negative effects of climate change on agriculture have only begun. Meeting the sustenance and nutritional needs of all people will require a concerted, multipronged global effort. Plant biologists can help in this effort. Over the past century breeding combined with improved agronomic practices have drastically increased crop yields. Continued yield growth will necessitate improving photosynthetic efficiency, yet until recently little attention was paid to mechanisms that might enhance photosynthesis.
Genetic variation in photosynthetic physiology
My dissertation was designed to determine if mesophyll conductance might prove useful for selecting crop cultivars with greater photosynthetic rates. Under the light saturated conditions typical of the upper leaf-layers in crop canopies, photosynthesis is limited by how quickly carbon dioxide diffuses from the atmosphere to the stroma inside chloroplasts. Stomatal conductance controls the rate of carbon dioxide diffusion into the leaf, and mesophyll conductance relates the ease of diffusion from the stomata through to the chloroplast interior. At the largest scale we know that mesophyll conductance varies appreciably across distantly related species, and that the variability in mesophyll conductance is coordinated with photosynthetic rates. At the smallest scale, plants with altered mesophyll conductance, but an otherwise uniform genetic background (via upregulation, or knock-outs of aquaporin genes facilitating movement of carbon dioxide through the chloroplast envelope), exhibit altered photosynthetic rates. It's not as clear what happens at the scale in-between these extremes. This is the scale where crop breeding takes place and we will need to improve photosynthesis. The specific focus of my dissertation is to understand if and how mesophyll conductance varies across genotypes of thin-leaved eudicots. I say thin-leaved eudicots because we know mesophyll conductance varies in rice, wheat, and barley (the most important monocot crops - corn utilizes a different photosynthetic pathway where mesophyll conductance is much less important), where it is also associated with photosynthetic rates. Globally half of the top ten most planted food crops are eudicots (in 2014; potato, bean, soybean, groundnut, and sweet potato) and mesophyll conductance has not been thoroughly studied in any of them. My work will determine if there is standing genetic variation for mesophyll conductance in soybean and Arabidopsis thaliana (there is). I want to know how that variation covaries with photosynthetic physiology more broadly, e.g. do genotypes with greater mesophyll conductance also have greater photosynthetic rates (yes!). Since there are no known mechanistic linkages between mesophyll conductance and water loss from the leaf we want to know if higher mesophyll conductance genotypes also have greater water use efficiency, which is dependent on the relationship between mesophyll and stomatal conductance.
Food security is a primary concern of mine. Roughly 1-in-8 people are classified as mal-nourished or undernourished today, global population continues to rise, and the negative effects of climate change on agriculture have only begun. Meeting the sustenance and nutritional needs of all people will require a concerted, multipronged global effort. Plant biologists can help in this effort. Over the past century breeding combined with improved agronomic practices have drastically increased crop yields. Continued yield growth will necessitate improving photosynthetic efficiency, yet until recently little attention was paid to mechanisms that might enhance photosynthesis.
Genetic variation in photosynthetic physiology
My dissertation was designed to determine if mesophyll conductance might prove useful for selecting crop cultivars with greater photosynthetic rates. Under the light saturated conditions typical of the upper leaf-layers in crop canopies, photosynthesis is limited by how quickly carbon dioxide diffuses from the atmosphere to the stroma inside chloroplasts. Stomatal conductance controls the rate of carbon dioxide diffusion into the leaf, and mesophyll conductance relates the ease of diffusion from the stomata through to the chloroplast interior. At the largest scale we know that mesophyll conductance varies appreciably across distantly related species, and that the variability in mesophyll conductance is coordinated with photosynthetic rates. At the smallest scale, plants with altered mesophyll conductance, but an otherwise uniform genetic background (via upregulation, or knock-outs of aquaporin genes facilitating movement of carbon dioxide through the chloroplast envelope), exhibit altered photosynthetic rates. It's not as clear what happens at the scale in-between these extremes. This is the scale where crop breeding takes place and we will need to improve photosynthesis. The specific focus of my dissertation is to understand if and how mesophyll conductance varies across genotypes of thin-leaved eudicots. I say thin-leaved eudicots because we know mesophyll conductance varies in rice, wheat, and barley (the most important monocot crops - corn utilizes a different photosynthetic pathway where mesophyll conductance is much less important), where it is also associated with photosynthetic rates. Globally half of the top ten most planted food crops are eudicots (in 2014; potato, bean, soybean, groundnut, and sweet potato) and mesophyll conductance has not been thoroughly studied in any of them. My work will determine if there is standing genetic variation for mesophyll conductance in soybean and Arabidopsis thaliana (there is). I want to know how that variation covaries with photosynthetic physiology more broadly, e.g. do genotypes with greater mesophyll conductance also have greater photosynthetic rates (yes!). Since there are no known mechanistic linkages between mesophyll conductance and water loss from the leaf we want to know if higher mesophyll conductance genotypes also have greater water use efficiency, which is dependent on the relationship between mesophyll and stomatal conductance.