The leaves of Arabidopsis thaliana are only a few millimeters long, but they hold some big questions. For his dissertation, Mick plans to answer a few of them, namely: Does polyploidy differentially affect a plant’s susceptibility to pathogens, and if so, is that due to a differential microbiome composition in polyploid plants?
More than 50 percent of all plant species, including A. thaliana, are polyploid, meaning that they have more than the usual number of pairs of chromosomes. These plants are often associated with novel or transgressive phenotypes, such as increased size and, potentially, different microbiomes. In fact, most major food crops are polyploid — including wheat, sugar cane, potatoes and bananas — implying the genetic condition’s practical the evolutionary advantages.
In humans, knowledge of the bacteria, fungi and other microbes in the gut has informed our understanding of healthy digestion and immune system responses, so could the same be true for plants and their ability to withstand pathogens and pests? Mick is planning to find out.
The answer starts with trays and trays of A. thaliana and a synthetic bacteria community created by Elijah Mehlferber in the Koskella lab. The 16 different bacteria composing this microbiome are sprayed onto the plants which are left to grow until the leaves are plucked and frozen for later observation and RNA -sequencing. For some of the plants, before the samples are collected, a pathogen is introduced to see how the plant will fare.
If all goes well, Mick will have his results in a few months. But in the meantime, he’s starting a second experiment to see if polyploidy and microbiomes can affect resistance to herbivores. A shipment of cabbage loopers (Trichoplusia ni), named for the way the moth larvae arch their backs into a loop when they crawl, is en route to the lab. It has been relatively well documented that animals avoid feeding on plants in the same family as Arabidopsis (Brassicaceae) — so with polyploid species like A. thaliana, Mick thinks herbivores may like it even less.
After an initial shipping snafu, Carrie’s Bomarea samples are now safe and sound at the University of Florida. As part of her PhD dissertation, Carrie is studying this tuberous, flowering genera of the plant family Alstroemeriaceae, including specimens of the species Bomarea edulis collected as she trekked across Mexico in 2018. The various cities she stopped in during her trip were representative of the habitat variation for B. edulis within Mexico — from Veracruz on the Gulf coast to Chiapas on the Pacific coast.
Forty-five of these samples, along with 147 others including 134 different species of Bomarea and close plant relatives, were shipped to Florida for DNA sequencing last week. Sequencing technologies like the ones used by the University of Florida’s GoFlag project summarize the atomic structure of the plant molecules, information which can be used to determine relationships between the different species. Once this data is available, Carrie will be able to construct a phylogeny, or a branching evolutionary history of these related plants.
This phylogenetic approach to understanding the evolution of different types of plants is important in determining biodiversity across landscapes, and this is what Carrie hopes to focus on during her postdoctoral studies.
Fundamentally she wants to understand how plants in the Bomarea genus are related to each other, using many samples per species to test whether each species is truly one evolutionary group or if there have been multiple evolutionary events leading to many different species which have been clumped together by botanists. Furthermore, Carrie plans to use the phylogeny she constructs at the end of her PhD to determine the extent to which Andean uplift has caused diversification of plants in the region.
Plants in the Bomarea genus occur frequently in the Andes, as well as in Mexico, Central America and the West Indies, preferring a cool, humid environment. In the Southern hemisphere, the Andes act as a barrier to atmospheric circulation, affecting the climate Bomarea species so carefully depend on. And, as the Nazca oceanic plate slides under the South American continental plate, the mountain range rises, sometimes in rapid growth spurts, affecting plant growth, evolution and the biodiversity of the landscape.