Arabidopsis thaliana copt transporters function in hormone metabolism and in metal stress

Resumen

Proper copper (Cu) homeostasis is required by living organisms to maintain essential cellular functions. In the model plant Arabidopsis thaliana, the high affinity Cu transporters (COPT) family play a key role in Cu transport under Cu deficiency conditions. In this thesis, we are going to study how affect an altered Cu transport to hormone metabolism and other metal homeostasis using different copt mutants. Plant hormone act as major endogenous cues that regulates morphological, physiological and molecular adaptive responses to environmental changes. Abscisic acid (ABA) is involved in plant responses to non-optimal environmental conditions, including nutrient availability. Since Cu is an important micronutrient, one objective of this thesis is unravel how ABA affects Cu uptake and distribution in plants subjected to different Cu availabilities. Also, we are going to study how the plant nutritional status can interfere with ABA biosynthesis and signalling mechanisms. Among of the results obtained, the exogenous ABA treatment inhibited COPT1, COPT2 and COPT6 expression and drastically modified COPT2-driven localization in roots. Cadmium (Cd) is a transition metal found naturally in the earth’s crust at trace levels, but its concentrations in the environment are rising due to human activities. Cd toxicity interferes with essential metal homeostasis, which is a problem for both plant nutrition and the consumption of healthy food by humans. Here, in this thesis, we are going to characterise the Cd toxicity effect on Cu homeostasis through the COPT5 transporter mutant. Three different processes which have been shown to affect Cd tolerance are altered in copt5 mutants. First, ethylene biosynthesis is affected in copt5 by Cd exposure. Second, Cu deficiency responses are attenuated under Cd treatment. Third, under long term treatments, oxidative stress symptoms are different in the roots and in the shoots. The interplay between iron (Fe) and Cu homeostasis in plants remain poorly understood. One objective in this thesis is the characterization of the copt5 mutant under Fe deficiency condition to analyse the interaction between Cu and Fe homeostasis. A global expression microarray analysis of the copt5 mutant points out the induction of Fe deficiency responses. COPT5 expression is altered under Fe deficiency and the copt5 mutant is sensitive to Fe deficiency. Probably as a consequence of its increased Cu and Fe deficiency responses, the copt5 mutant displays reduced activity of both Cu- and Fe-dependent superoxide dismutases. Moreover, the copt5 mutant mobilizes its Fe storage pools faster and contains more Fe in cotyledons and seeds. These results underline the importance of internal metal pools in the control of Cu and Fe deficiency responses and their crosstalk, which are critical for governing proper plant development in response to combined metal scarcities in soils.