After years in the making, this paper is finally out, and showcases a wonderful and ongoing collaboration with Guillaume Théroux-Rancourt.
Our 2018 PLoS Biology paper showed that genome downsizing was critical to shrinking cell sizes and elevating cell packing densities, enabling Cretaceous angiosperms to elevate their leaf surface conductance and gas exchange rates.
In the present paper, now published in Proceedings of the Royal Society B, we show that genome downsizing has implications beyond the leaf surface to influence the structure of the mesophyll tissue responsible for photosynthesis. Genome size, therefore, is a strong predictor of cell sizes and cell packing densities in all leaf tissues. Furthermore, reductions in genome size and cell size are necessary to increase the conductance of the mesophyll tissue.
We show that cell size–and not mesophyll porosity, as is commonly thought–is a much stronger predictor of the three-dimensional surface area of the mesophyll tissue that limits mesophyll conductance. Furthermore, the two layers of mesophyll (spongy and palisade) that occur in most species have divergent structures associated with their different functions and with the resource gradients (light and CO2) that occur across them.
The paper is available here.