Resumen de RNA-SEQ identifies two Arabidopsis genes required for copper acquisition and a copper dependence of iron homeostasis
María Bernal, David Casero Díaz-Cano, Vasantika Singh, Arne Grande, Huijun Yang, Erin Connolly, Peter Huijser, Matteo Pellegrini, Sabeeha Merchant, Ute Krämer
The transition metal copper (Cu) is an essential element for all living organisms. In plants, Cuplays key roles in photosynthetic electron-transport chains in chloroplasts and mitochondria, aswell as in cell wall metabolism, ethylene perception, molybdenum cofactor synthesis andoxidative stress protection. Because of its physiological importance, suboptimal concentrationsof Cu trigger a re-organization of metabolism for Cu economy, and pronounced Cu deficiencycauses severe growth and fertility defects. However, when present in excess, Cu can be highlytoxic. Therefore, Cu uptake, utilization and cellular concentrations are strictly regulated. Anumber of components of the Cu-homeostatic network of Arabidopsis have been alreadyidentified, however, the mechanisms that control plant gene expression responses to Cudeficiencyare poorly understood. In Chlamydomonas reinhardtii, the transcription factor Crr1 isrequired for activating and repressing the expression of a number of genes in response to Cudeficiency. This protein contains a plant-specific DNA-binding domain (SBP domain), ankyrinrepeats and a C-terminal cysteine-rich region with similarity to a Drosophila metallothionein(MT). In Arabidopsis, there is a family of 17 proteins with SBP domains named SPL family(SBP-like) of which a subset of proteins have been implicated in flowering time control andfloral development. Among all of them, AtSPL7 is the most similar to Crr1 (27 % identity), andAtSPL1 (25 % identity), AtSPL12 (24 % identity) and AtSPL14 (23 % identity) share the sameprotein architecture. A recent publication has shown that AtSPL7 regulates the expression ofnumerous genes in response to Cu-deficiency (Yamasaki et al., 2009). The goal of this work isto further investigate the role of SPL7 in the regulation of Cu deficiency responses. For thispurpose, three independent experiments have been carried out including wild-type and spl7mutant plants growing in Cu sufficient and Cu deficient hydroponic media, respectively. Wehave used RNA-Seq to identify genes with altered expression in response to Cu-deficiency inboth roots and shoots. Among the candidate genes identified, we found that FRO4 and FRO5expression is regulated dependent on SPL7 under Cu-deficiency conditions, and they encodeCu(II)-specific root surface reductases of the Cu uptake machinery. We have also investigatedwhether there is a connection between Cu and iron (Fe) homeostasis in plants as inchlamydomonas, yeast and humans. We have observed that copper deficiency causes iron (Fe)deficiency and defects in Fe root-to-shoot partitioning most likely due to the loss-of-function ofa multicopper-oxidase that might play a key role in Fe homeostasis.
