CEB - Centre of Biological Engineering, University of Minho, Campus of Gualtar, Braga, Portugal; CBMA - Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campus of Gualtar, Braga, Portugal. CBMA - Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campus of Gualtar, Braga, Portugal. CEB - Centre of Biological Engineering, University of Minho, Campus of Gualtar, Braga, Portugal. Electronic address: artur@deb.uminho.pt.