Thread by @spklein2

The manuscript on integrated #maize #root phenotypes under #drought is now available online from @PlantPhys! Before you head there, here's a little summary on what this paper is all about:

plantphysiol.org/content/early/…

But before I do that, I want to thank the other co-authors, my labmates, collaborators, advisors, funding sources and everyone else involved in this massive root phenotyping effort. None of this would have been possible without their support!

To start, what exactly is an "integrated phenotype"? Tons of awesome work has demonstrated the value of individual traits (or phenes) for performance under stressful conditions. But biology teaches us, “it’s actually more complicated than that.”

So, in this project we wanted to identify combinations of root phenes, or “integrated root phenotypes” that were related to enhanced performance of maize under drought.

Some combos were proposed by the "Steep, Cheap and Deep" ideotype. academic.oup.com/aob/article/11…

We phenotyped the root architecture and root anatomy of 400 genotypes of the Wisconsin Diversity Panel under well-watered and water-stressed conditions and found that root phenotypes are highly variable.

Look how pretty these roots are!

First, we performed a phenotypic bulked segregant analysis to compare the average root phenotype of the most drought tolerant (best bulk) and drought sensitive (worst bulk) maize lines. These bulks performed similarly under normal conditions.

Under water stress, the roots of the best bulk, on average, were thicker, contained increased aerenchyma content, larger cortical cells in arranged in a larger number of files…

The best bulk also appeared to be "water savers" - on average the best performers contained an increased number of narrower metaxylem vessels, which resulted in a dramatic reduction in hydraulic conductance.

Meanwhile, the worst bulk was like...

Second, we used PAM clustering to identify unique integrated root phenotypes across the whole panel. For this part, we sorted the genotypes into 3 phenology groups a priori to account for differences in water usage.

We identified several clusters of root phenotypes with varying levels of performance and began to see patterns for integrated phenotypes that were consistently related to improved performance under drought.

Those integrated phenotypes may be related to these beneficial characteristics:

1. Reducing cortical metabolic maintenance costs

A cortex containing greater aerenchyma content and large cells is less costly to maintain. C can be re-allocated elsewhere (e.g. root construction).

2. Restricting uptake of water to conserve soil moisture

This relates mostly to xylem-related phenes. Clusters with smaller metaxylem vessels and generally reduced hydraulic conductance. Though, this characteristics wasn't as important for early flower-ers.

3. Improving penetrability of hard, dry soils

A root with a proportionally large stele and small cells in the distal cortex may increase penetrability in a soil that hardens as it dries.

Each of the clusters that performed well under drought exhibited at least one of these beneficial characteristics, but no cluster showed all 3.

Also discussed: phene synergistic/antagonistic interactions, role of plasticity, and what this means for ideotype breeding.

That's the manuscript in a nutshell! Feel free to reach out if you have questions. The root phenotype data will be available on @ZENODO_ORG shortly.

Thanks for stopping by!