Adaptation to Drought in Populus: Is Leaf Growth a Key Trait?

Extreme genotypes originating from latitudes of contrasting precipitation and temperature environments were selected from a population of more than 500 wild black poplar genotypes. These three genotypes of P. nigra show distinct phenotypic differences in leaf development and water use efficiency, as measured through carbon isotope discrimination. The Spanish genotype has small leaves which contain large cells with low stomatal density, while the Italian genotype has large leaves made up of many small cells with high stomatal density.  Furthermore, these genotypes vary in their drought adaptation strategies due to the variability in water availability at the geographic origin of the genotype. Under water deficit, the Spanish genotype demonstrated increased water use efficiency, while the Italian genotype had a reduced water use efficiency.

In WATBIO, we have used RNA-seq alongside extensive phenotyping, to dissect drought adaptation in these three genotypes of P. nigra. These genotypes show markedly different genetic architecture with 3352 genes differentially expressed between the Spanish and Italian extreme genotypes. Furthermore, the clones show clear differences in their response to drought with 456 genes differentially expressed between the Spanish and Italian genotypes under drought compared to controlled conditions. We have identified mechanisms which maintain growth when water availability is low through the investigation of tissue and organ development at increasing levels of drought intensity over time using single end sequencing. Understanding this natural genetic variation in Populus will make it possible to produce improved germplasm for sustainable biomass production in terms of water use efficiency, biomass production and lignocellulosic quality.