Cutting edge: Desiccation tolerance explored through genomes and transcriptomes

X. viscosa (photo by C. Whitehouse)

Resurrection plants are a diverse and unique group of angiosperms able to tolerate desiccation to the point of being air-dry at low humidity, sometimes for years. They appear to be dead, and then to “spring back to life” with only a slight bit of moisture, turning green and robust in a few hours.

The interest of researchers in this group has grown considerably in the last 20 years. Recently, the publication of genome sequences of three resurrection species (Boea hygrometrica, Oropetium thomaeum and Xerophyta viscosa) and high throughput transcriptome studies has made available precious resources for current and future studies. To this date, the best studied resurrection genera at the ecological and physiological levels are Xerophyta, Craterostigma and Myrothamnus.  This is the first of that group to also have a sequenced genome.

In this paper, the authors report the genome of the resurrection plant species Xerophyta viscosa, recently sequenced by an international consortium of researchers from the Netherlands, South Africa, USA, Australia and Germany. In addition, making this paper truly cutting edge, they report a comprehensive gene expression analysis as the plants dried, desiccated and revived. Going well beyond most plant sequencing papers, the study reveals a genetic footprint of progress through this complex sequence.

Henk Hilhorst of Wageningen University & Research and leader of this research, said: “Food crops that can survive extreme drought are, and will be, of increasing importance. Climate change causes longer and more extreme periods of drought, while at the same time the growing world population demands a dramatic increase of food production. Resurrection species like X. viscosa may serve as ideal models for the ultimate design of crops with enhanced drought tolerance.”

Xerophyta viscosa is native to southern Africa where it inhabits rocky terrains in exposed grasslands and frequently experiences periods of severe water deficit. It can survive the loss of 95% of its total cellular water, dismantling its photosynthetic apparatus during dehydration to avoid photo-oxidative damage. During rehydration, within only three days, it restores normal metabolism and photosynthetic activity.

The researchers highlighted the remarkable resemblance between the process of leaf desiccation tolerance and well-characterized seed maturation mechanisms, including the activation of certain protection mechanisms and signaling pathways.

Maria-Cecília Costa (currently a post-doc fellow of the Plant Stress Lab of the University of Cape Town) studied desiccating plants and the associated gene expression patterns. She hypothesized: “ X. viscosa may well have acquired its desiccation tolerance from ancestors that evolved genes that allow seeds to survive drying.”

X. viscosa has now joined the short, but growing list of sequenced resurrection plant genomes, including the grass Oropetium thomaeum and the eudicot Boea hygrometrica. The wealth of genomic resources in these species – together with transcriptomic analyses through desiccation cycles – provides an opportunity to finally test hypotheses for the convergent evolution of desiccation tolerance in the different lineages of resurrection plants. If such research will indeed lead to more drought tolerant crops, it will be through understanding both of discrete elements of desiccation-tolerance pathways, and of the networks in which those elements are embedded.

 

Citation:

Costa M-ClD, Artur MAS, Maia J, Jonkheer E, Derks MFL, et al. (2017) – Nature Plants 3, Article number: 17038. doi:10.1038/nplants.2017.38 PMID: 28346448

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