ABSTRACT
Potato is a drought-sensitive crop whose global sustainable production is threatened by alterations in water availability. Whilst ancestral Solanum tuberosum Andigenum landraces retain wild drought tolerance mechanisms, their molecular bases remain poorly understood. In this study, an aeroponic growth system was established to investigate stress responses in leaf and root of two Andigenum varieties with contrasting drought tolerance. Comparative transcriptome analysis revealed widespread differences in the response of the two varieties at early and late time points of exposure to drought stress and in the recovery after rewatering. Major differences in the response of the two varieties occurred at the early time point, suggesting the speed of response is crucial. In the leaves and roots of the tolerant variety, we observed rapid upregulation of ABA-related genes, which did not occur until later in the susceptible variety and indicated not only more effective ABA synthesis and mobilization, but more effective feedback regulation to limit detrimental effects of too much ABA. Roots of both varieties showed differential expression of genes involved in cell wall reinforcement and remodeling to maintain cell wall strength, hydration and growth under drought stress, including genes involved in lignification and wall expansion, though the response was stronger in the tolerant variety. Such changes in leaf and root may help to limit water losses in the tolerant variety, while limiting the reduction in photosynthetic rate. These findings provide insights into molecular bases of drought tolerance mechanisms and pave the way for their reintroduction into modern cultivars with improved resistance to drought stress and yield stability under drought conditions.
ABSTRACT
Branched-chain amino acids (BCAAs) are three of the nine essential amino acids in human and animal diets and are important for numerous processes in development and growth. However, seed BCAA levels in major crops are insufficient to meet dietary requirements, making genetic improvement for increased and balanced seed BCAAs an important nutritional target. Addressing this issue requires a better understanding of the genetics underlying seed BCAA content and composition. Here, a genome-wide association study and haplotype analysis for seed BCAA traits in Arabidopsis thaliana revealed a strong association with a chromosomal interval containing two branched-chain amino acid transferases, BCAT1 and BCAT2. Linkage analysis, reverse genetic approaches, and molecular complementation analysis demonstrated that allelic variation at BCAT2 is responsible for the natural variation of seed BCAAs in this interval. Complementation analysis of a bcat2 null mutant with two significantly different alleles from accessions Bayreuth-0 and Shahdara is consistent with BCAT2 contributing to natural variation in BCAA levels, glutamate recycling, and free amino acid homeostasis in seeds in an allele-dependent manner. The seed-specific phenotype of bcat2 null alleles, its strong transcription induction during late seed development, and its subcellular localization to the mitochondria are consistent with a unique, catabolic role for BCAT2 in BCAA metabolism in seeds.
