Why some grasses got better photosynthesis

Brown University News: Even on the evolutionary time scale of tens of millions of years there is such a thing as being in the right shape at the right time. An anatomical difference in the ability to seize the moment, according to a study led by Brown University biologists, explains why more species in one broad group, or clade, of grasses evolved a more efficient means of photosynthesis than species in another clade.

Biologists refer to the grasses that have evolved this better means of making their food in warm, sunny, and dry conditions with the designation “C4.” Grasses without that trait are labeled “C3.” What scientists had already known is that while all of the grasses in the BEP and PACMAD clades have the basic metabolic infrastructure to become C4 grasses, the species that have actually done so are entirely in the PACMAD clade. A four-nation group of scientists wondered why that disparity exists.

To find out, Brown postdoctoral researcher and lead author Pascal-Antoine Christin spent two years closely examining the cellular anatomy of 157 living species of BEP and PACMAD grasses. Using genetic data, the team also organized the species into their evolutionary tree, which they then used to infer the anatomical traits of ancestral grasses that no longer exist today, a common analytical technique known as ancestral state reconstruction. That allowed them to consider how anatomical differences likely evolved among species over time.

…Erika Edwards“Now that we have this increasingly detailed bird’s-eye view, we can start to become a more predictive science. ... In terms of genetic engineering we’re going to be able to provide some useful information to people who want to improve species, such as important crops.”

“Now that we have this increasingly detailed bird’s-eye view, we can start to become a more predictive science. ... In terms of genetic engineering we’re going to be able to provide some useful information to people who want to improve species, such as important crops.” Credit: Mike Cohea/Brown UniversityIn C4 plants, such an anatomical arrangement facilitates a more efficient transfer and processing of CO2 in the bundle sheath cells when CO2 is in relatively short supply. When temperatures get hot or plants become stressed, they stop taking in as much CO2, creating just such a shortage within the leaf…

A grassland in Canastra, Brazil, shot by BDG2007, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license