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Abscisic acid promotes pre-emergence stages of lateral root development in Medicago truncatula.

ABSTRACT: The plant root system is important for plant anchorage and nutrition. Among the different characteristics of the root system, root branching is a major factor of plasticity and adaptation to changing environments. Indeed, many biotic and abiotic stresses, such as drought or symbiotic interactions, influence root branching. Many studies concerning root development and root branching were performed on the model plant Arabidopsis thaliana, but this model plant has a very simplified root structure and is not able to establish any symbiotic interactions. We have recently described 7 stages for lateral root development in the model legume Medicago truncatula and found significant differences in the tissular contribution of root cell layers to the formation of new lateral roots (LR). We have also described 2 transgenic lines expressing the DR5:GUS and DR5:VENUS-N7 reporter genes that are useful to follow LR formation at early developmental stages. Here, we describe the use of these transgenic lines to monitor LR developmental responses of M. truncatula to the phytohormone abscisic acid (ABA) which is a major actor of stress and symbiotic interactions. We show that ABA promotes the formation of new lateral root primordia and their development, mostly at the late, pre-emergence stage.

SUBMITTER: Gonzalez AA

PROVIDER: S-EPMC4623335 | biostudies-other | 2015

REPOSITORIES: biostudies-other

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Project description:Enhancing the knowledge on the genetic basis of germination and heterotrophic growth at extreme temperatures is of major importance for improving crop establishment. A quantitative trait loci (QTL) analysis was carried out at sub- and supra-optimal temperatures at these early stages in the model Legume Medicago truncatula. On the basis of an ecophysiological model framework, two populations of recombinant inbred lines were chosen for the contrasting behaviours of parental lines: LR5 at sub-optimal temperatures (5 or 10°C) and LR4 at a supra-optimal temperature (20°C). Seed masses were measured in all lines. For LR5, germination rates and hypocotyl growth were measured by hand, whereas for LR4, imbibition and germination rates as well as early embryonic axis growth were measured using an automated image capture and analysis device. QTLs were found for all traits. The phenotyping framework we defined for measuring variables, distinguished stages and enabled identification of distinct QTLs for seed mass (chromosomes 1, 5, 7 and 8), imbibition (chromosome 4), germination (chromosomes 3, 5, 7 and 8) and heterotrophic growth (chromosomes 1, 2, 3 and 8). The three QTL identified for hypocotyl length at sub-optimal temperature explained the largest part of the phenotypic variation (60% together). One digenic interaction was found for hypocotyl width at sub-optimal temperature and the loci involved were linked to additive QTLs for hypocotyl elongation at low temperature. Together with working on a model plant, this approach facilitated the identification of genes specific to each stage that could provide reliable markers for assisting selection and improving crop establishment. With this aim in view, an initial set of putative candidate genes was identified in the light of the role of abscissic acid/gibberellin balance in regulating germination at high temperatures (e.g. ABI4, ABI5), the molecular cascade in response to cold stress (e.g. CBF1, ICE1) and hypotheses on changes in cell elongation (e.g. GASA1, AtEXPA11) with changes in temperatures based on studies at the whole plant scale.

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Abscisic acid promotes pre-emergence stages of lateral root development in Medicago truncatula.

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