Abstract
BackgroundResequencing can be used to identify genome variations underpinning many morphological and physiological phenotypes. Legume model plant Medicago truncatula ecotypes Jemalong A17 (J. A17) and R108 differ in their responses to mineral toxicity of aluminum and sodium, and mineral deficiency of iron in growth medium. The difference may result from their genome variations, but no experimental evidence supports this hypothesis.ResultsA total of 12,750 structure variations, 135,045 short insertions/deletions and 764,154 single nucleotide polymorphisms were identified by resequencing the genome of R108. The suppressed expression of MtAACT that encodes a putative aluminum-induced citrate efflux transporter by deletion of partial sequence of the second intron may account for the less aluminum-induced citrate exudation and greater accumulation of aluminum in roots of R108 than in roots of J. A17, thus rendering R108 more sensitive to aluminum toxicity. The higher expression-level of MtZpt2-1 encoding a TFIIIA-related transcription factor in J. A17 than R108 under conditions of salt stress can be explained by the greater number of stress-responsive elements in its promoter sequence, thus conferring J. A17 more tolerant to salt stress than R108 plants by activating the expression of downstream stress-responsive genes. YSLs (Yellow Stripe-Likes) are involved in long-distance transport of iron in plants. We found that an YSL gene was deleted in the genome of R108 plants, thus rendering R108 less tolerance to iron deficiency than J. A17 plants.ConclusionsThe deletion or change in several genes may account for the different responses of M. truncatula ecotypes J. A17 and R108 to mineral toxicity of aluminum and sodium as well as iron deficiency. Uncovering genome variations by resequencing is an effective method to identify different traits between species/ecotypes that are genetically related. These findings demonstrate that analyses of genome variations by resequencing can shed important light on differences in responses of M. truncatula ecotypes to abiotic stress in general and mineral stress in particular.
Highlights
Resequencing can be used to identify genome variations underpinning many morphological and physiological phenotypes
Exposure to salt stress led to reductions in K+ concentrations in shoots of both ecotypes, and the salt stress-induced reduction in K+ concentration was greater in R108 than in J
The two M. truncatula ecotypes Jemalong A17 and R108 differed in their sensitivity to aluminum toxicity, salt stress and iron deficiency
Summary
Resequencing can be used to identify genome variations underpinning many morphological and physiological phenotypes. Legume model plant Medicago truncatula ecotypes Jemalong A17 A17) and R108 differ in their responses to mineral toxicity of aluminum and sodium, and mineral deficiency of iron in growth medium. As a model legume species, Medicago truncatula Gaertn has been widely used to study functional genomics because of its small diploid genome, self-fertility, short generation cycle and easy transformation [6]. The two ecotypes exhibit different tolerance to salt stress, such that ecotype J. Further studies reveal that a TFIIIA-related transcription factor gene, MtZpt shows different expression in the two ecotypes, and that overexpression of MtZpt in roots confers enhanced tolerance to salt stress [14,15]. Our previous work revealed that the two ecotypes differed in their tolerance to deficiency in mineral nutrients. Despite the morphological and physiological differences between the two ecotypes, few studies have investigated the molecular mechanisms underlying the differences due to lack of information on the genome of R108
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