Abstract
Forage legumes are an important livestock nutritional resource, which includes essential metals, such as copper. Particularly, the high prevalence of hypocuprosis causes important economic losses to Argentinian cattle agrosystems. Copper deficiency in cattle is partially due to its low content in forage produced by natural grassland, and is exacerbated by flooding conditions. Previous results indicated that incorporation of Lotus spp. into natural grassland increases forage nutritional quality, including higher copper levels. However, the biological processes and molecular mechanisms involved in copper uptake by Lotus spp. remain poorly understood. Here, we identify four genes that encode putative members of the Lotus copper transporter family, denoted COPT in higher plants. A heterologous functional complementation assay of the Saccharomyces cerevisiae ctr1∆ctr3∆ strain, which lacks the corresponding yeast copper transporters, with the putative Lotus COPT proteins shows a partial rescue of the yeast phenotypes in restrictive media. Under partial submergence conditions, the copper content of L. japonicus plants decreases and the expression of two Lotus COPT genes is induced. These results strongly suggest that the Lotus COPT proteins identified in this work function in copper uptake. In addition, the fact that environmental conditions affect the expression of certain COPT genes supports their involvement in adaptive mechanisms and envisages putative biotechnological strategies to improve cattle copper nutrition.
Highlights
Copper (Cu) is an essential micronutrient for all living organisms because it participates as a cofactor in biological processes, such as respiration, photosynthesis, carbon and nitrogen metabolism, and oxidative stress protection [1]
In order to study the effects of flooding stress into different accessions of the Lotus genus, one-month old plants were cultivated under partial submergence for 42 days under greenhouse experimental conditions mimicking soil and irrigation flooding suffered in the Flooding Pampa (FP)
Even if all evaluated genotypes showed similar symptoms when grown under this treatment, plants from Lotus japonicus (Lj) and L. corniculatus tetraploid (LcT) showed the most marked effects compared to others under similar conditions
Summary
Copper (Cu) is an essential micronutrient for all living organisms because it participates as a cofactor in biological processes, such as respiration, photosynthesis, carbon and nitrogen metabolism, and oxidative stress protection [1]. Species richness decreases in flood-prone regions with alkaline or saline soils [7] Under these conditions, the main food source for cattle are natural grasslands [6], which produce a low quality forage since they are dominated by grasses, with very few legumes. COPT3 participates in pollen grains and vascular bundles’ Cu transport [33]; and COPT5 is mainly located in the tonoplast of vascular bundles of the root cells and in the siliques, and functions in Cu storage in the vacuoles [30], affecting Fe homeostasis in this compartment [34] Some of these proteins have been characterized in the species of agronomical interest. The L. japonicus COPT protein family has been characterized and their expression response to partial submergence conditions has been evaluated in order to dissect their putative roles in Cu uptake
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