Various responses to Zinc deficiency among accessions of the grass model Brachypodium distachyon

Zinc (Zn) is an essential micronutrient for plants. In their environment, plants are often exposed to limited Zn supply i in soils. Indeed, soils deficient in Zn cover a large surface of arable lands, including many densely populated and poor areas around the world. Zn deficiency lower plant performance and crop yield, but also severely impacts human health. To a certain extent, Zn homeostasis mechanisms allow plants to maintain Zn concentrations in tissues within physiological limits in response to Zn deficiency. These mechanisms have been mostly examined in Arabidopsis and in rice, and translation to pooideae crops is lagging behind. Here, we exploit the natural diversity found in Brachypodium distachyon (Brachypodium) as a model to address this question. Brachypodium accessions mostly evolved around the Mediterranean region, which is characterized by highly variable Zn availability in soils. First, we developed two growth systems enabling the manipulation of Zn supply in Brachypodium: (i) a circulating hydroponic system for seed-to-seed development, where Zn supply can be finely adjusted; and (ii) a soil with increased pH (using CaO), which decreases Zn and other nutrients availably, mimicking soil conditions encountered in the field. Plants of 15 Brachypodium accessions were grown in these conditions for 6 weeks. Germination rate, biomass production or leaf number were quantified, and root and shoot tissues were collected for ionome and gene expression profiling using ICP-AES and quantitative RT-PCR, respectively. This phenotyping revealed extensive variation among accessions for several traits. Leveraging this natural variation should enable a better understanding of Zn homeostasis in Brachypodium.