Molecular mechanisms underlying plant adaptations to extreme environments

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The world's population is expected to exceed 9 billion by 2050. With a finite global land base for agriculture, we face huge uncertainties in how we can feed 2.5 billion more people. We must produce more food with less land but a concurrent challenge is the increasing frequency of unpredictable, severe episodes of adverse weather, conditions already leading to yield loss and catastrophic crop failures. We must find more effective ways of stabilizing yields and ensuring a secure and safe food supply, ideally involving fewer costly inputs like irrigation, fertilizers and crop protection chemicals. However, research identifying traits to improve crop stress tolerance has enjoyed few commercialization success stories. We typically source tolerance traits within crop species or in model plants that have either already lost their tolerance genes through successive breeding for yield and/or the plants never had those tolerance traits to begin with. The advent of high through-put sequencing now allows us to cast a wider net for finding tolerance traits and our approach exploits a wild crop-relative adapted to extreme conditions, an "extremophyte", to identify tolerance traits and their genetic basis. Eutrema salsugineum is a plant that is closely related to canola but thrives on highly saline, alkaline soil. We discovered that an ecotype found in the Yukon, Canada, displays exceptional tolerance to drought and it thrives on soil that has low levels of the essential plant nutrient, phosphate. In contrast, an ecotype from Shandong, China, is far less tolerant to both drought and low phosphate. This differential sensitivity offers a means of identifying the genetic basis conferring tolerance versus sensitivity to drought and low phosphate. We will deploy an exceptional genetic resource comprising 180 recombinant inbred mapping populations (RILs) that were produced by crossing Yukon and Shandong E. salsugineum parents. We will use a combination of Restriction site Associated DNA sequencing analysis of these RILs, bioinformatics, and down-stream validation by gene editing followed by phenotypic profiling to identify regions of genes in the E. salsugineum genome associated with efficient use of phosphate as an initial objective, and in a second objective, tolerance to water deficits. Typically, plants on low phosphate have shorter roots to forage more effectively for phosphate in upper soil layers where it is more plentiful. However, roots penetrating deeply into soil profiles are needed to reach receding water during drought. An intriguing feature of Yukon E. salsugineum is that a tolerance to low phosphate is not accompanied by shorter roots. Canada, like much of the world, is facing a future of drier overall summers and dwindling global supplies of accessible rock phosphate for fertilizers, a combination of challenges that Yukon E. salsugineum already copes with successfully in its natural habitat using traits we urgently need on the farm.