Modifications of Source-Sink Relationships and the Development of Stress-Tolerant Brachypodium

Modifications of Source-Sink Relationships and the Development of Stress-Tolerant Brachypodium

Nir Sade¹, , Maria Rubio Wilhelmi¹, Wagner De Souza¹, Matthew Wright¹,Elias Bassil¹, Lifeng Liu², John Vogel², and Eduardo Blumwald¹

¹Department of Plant Sciences University of California, Davis, CA 95616 USA
²DOE Joint Genome Institute, Department of Plant and Microbial Biology, UC Berkeley, Walnut Creek, CA 94598 USA

Environmental stresses are the most serious factors limiting the productivity of agricultural crops. Recent studies have linked the increased frequency of severe abiotic stress events with global warming, emphasizing the urgent need to develop crops with enhanced tolerance to abiotic stresses. Abiotic stress tolerance is particularly important for biomass crops because they must be grown under low-input conditions to maximize the net carbon ratio and on marginal land to minimize competition with food crops. We aim at the development of modules comprising several complementary genes that can be used to engineer stress tolerance into biomass perennial model crops such as Brachypodium sylvaticum. Toward this goal, we examined the salt and freezing tolerance of several wild type B. sylvaticum lines to determine optimal varieties that could be used as our transgene background. We identified a sensitive (i.e AIN1)  and a tolerant varieties (i.e GRE1)  for salt and freezing tolerance. GRE1 displayed better biomass and carbon assimilation under high salinity and improved survival under freezing. Preliminary results suggested that sodium compartmentation to the vacuole might be enhanced in GRE1 under stress and this phenomena was well correlated with the expression of a vacuolar NHX1 antiporter. Moreover, vacuolar pH under salt stress  was more stable in GRE1 as compared to AIN1.  Constitutive over expression of AtNHX1 in the salt sensitive AIN1 background conferred salt tolerance. Quantification of the freezing tolerance of GRE1 and AIN1 will be also presented and discussed.

In the effort to develop broad biotechnological tools for the improvement of perennial grasses, we completed the transformation of AIN1 B. sylvaticum with constructs containing 33 genes shown to be associated with enhanced abiotic stress tolerance and source-sink relationships in monocots. Single and/or combination of those genes were overexpressed using either constitutive or stress inducible promoters. We have generated single copy insert homozygous T₂ lines for all constructs. The response of those transgenes lines to various abiotic stresses is being tested.