As the impact of global warming deepens, drought, it appears, is the new normal. Deserts are bulging past their historical boundaries, and rainfall is becoming more erratic; these developments, coupled with the ever-increasing human population, present a challenging future for the global food supply.
In order to maintain the food supply we’ve come to demand and increase capacity for future populations, a massive shift in global agriculture is required. “We’re going to have to grow more crops in more drought prone areas,” explains molecular biologist Jill Farrant, speaking at the Falling Walls Conference in Berlin in November, “and to this point, that hasn’t been possible.” Fortunately, plants are relatively robust in low-water conditions: while animals and microbes die upon loss of 1-10% of their total water content, plants can generally handle 10-45% water loss. Some plants are even better, finding ways to strategically avoid water stressed conditions (shrubs that grow only during the rainy season) or hold on to scarce liquid when it’s there (water-retaining plants like cacti).
However, neither of these lifestyle choices is transferable to crops that provide the bulk of the planet’s calories, like corn or wheat. You’ve got to go deeper, to deconstruct the genetic instructions that allow the superstars of drought resistance to come back from near complete desiccation. This is precisely what Farrant and her global network of collaborators has been doing over the last several years. They’ve identified nearly a dozen plants – flowers and ferns – that can lose up to 95% of their water content and begin growth anew upon rehydration.
To figure out the molecular secrets that keep these evocatively named “resurrection plants” ticking, Farrant and her team undertook a systems biology approach. With an arsenal of analytical power behind them, the researchers extracted and sequenced DNA, RNA, proteins, metabolites, and lipids produced under normal, water-rich conditions, as well as during water-stressed situations. By comparing the differences, the thinking went, it would be possible to see which cellular products enable these remarkable plants to come back from the dead.
Among the metabolites that are more abundant in dry conditions: heat shock proteins (a range of products made under stressful conditions), chaperonins (which help other proteins fold), antioxidants (which sop up damaging free radicals), and the mysterious leaproteins. This latter class of products – “weird little proteins that are completely disordered in aqueous solution” – was particularly intriguing to Farrant. “We still don’t know exactly what they do, but they probably stabilize structures, like antioxidants. And the really cool part is that they only form their functional 3-D structure in the dry state,” implying that they not only can survive low-water conditions, but may well require them.
The presence of certain metabolites, however, doesn’t tell the whole story: just because it’s there, “doesn’t mean it’s active,” cautions Farrant, “and we’d like to know when or where it might be active.” There’s also the other side of the expression equation: “We tend to think that if something’s upregulated, it must be needed,” explains Farrant, “but what about all of those downregulated things that they have to decrease because they could be damaging? Not enough of us are thinking about what needs to be switched off.” For example, certain metabolisms are likely halted because they are too energetically expensive, or because a malfunction caused by water stress could be catastrophic.
Ultimately, as Farrant and her team work to understand the full resurrection plant system (they’re beginning to incorporate the microbial community as well), applications for a rapidly changing world might not be too far behind. In some situations, it may be best to insert genes from resurrection plants into certain crops, but often, the capabilities appear to already be in place, dormant in the genome. “There are plenty of things we’re seeing that are important in drought tolerance,” explains Farrant, “and normal plants have them too, they just don’t switch them on at the right time.”
If these types of protective genes can be expressed in crops, we might be a step closer to avoiding drastic food shortages in an era of persistent drought.
