Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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K. Gasic and S.S. Korban
In plants, different members of the Cu chaperone family have been identified
and characterized, including an Arabidopsis CCH (Himelblau et al., 1998) and AtCOX17
(Balandin and Castresana, 2000), and a tomato LYS7 (Zhu et al., 2000). Beyond the CCH
gene (Mira et al., 2001), there is no information available on the expression of COX17
and CCS (Wintz and Vulpe, 2002) genes in different plant organs and tissues and/or
during plant development. However, Trinidade et al. (2003) have isolated and characterized
a potato Cu chaperone gene StCCS, coding for the Cu/Zn superoxide dismutase
(Sodp). Furthermore, they analyzed its expression throughout various tissues of a
potato plant, and during tuberization.
4.3. Transporters
4.3.1. ABC – Type Family
The ATP binding cassette (ABC) protein superfamily is the largest membrane protein
family known in both prokaryotes and eukaryotes, including microbes, plants, and
animals. Members of this superfamily catalyze the MgATP-energized transport of a
broad range of substrates across biological membranes. Extensive reviews have been
written on plant ABC transporters (Theodoulou, 2000), and a complete inventory of
ABC proteins in Arabidopsis have been compiled (Sanchez-Fernandez et al., 2001).
Isolation of IDI7, an Fe-deficiency-induced cDNA, from roots of barley was
reported (Yamaguchi et al., 2002). Phylogenetic analysis revealed that IDI7 was closely
related to the half-type ABC protein subfamily, which included mammalian transporters
associated with antigen processing (TAPs). IDI7 and its orthologues seemed to comprise
a new class of ABC transporters located in the tonoplast of higher plants. Accumulation
of IDI7 mRNA was much lower under higher concentrations of heavy metals
than under Fe-deficiency conditions, thus suggesting its lack of involvement in the
sequestration of metal ions into vacuoles.
Shikanai et al. (2003) have characterized six Arabidopsis mutants defectivein
the PAA1 gene which codes for a member of the metal-transporting P-type ATPase
family with a functional N-terminal chloroplast transit peptide. PAA1 is a critical component
of a Cu transport system in chloroplasts responsible for cofactor delivery to the
plastocyanin and the Cu/ZnSOD. It has been reported that paa1 mutants exhibit highchlorophyll-fluorescence
phenotypes due to impairment of the photosynthetic electron
transport possibly ascribed to decreased levels of holoplastocyanin. Chloroplastic
Cu/ZnSOD activity is also reduced in paa1 mutants, thus suggesting that PAA1
mediates Cu transfer across the plastid envelope (Fig. 1).
Arababopsis thaliana has eight genes encoding members of the type 1 B
heavy
metal–transporting subfamily of the P-type ATPases (Hussain et al., 2004) (Table 1).
Three of these transporters, HMA2, HMA3, and HMA4, are closely related to each
other and have high sequence similarity to the divalent heavy metal cation transporters