Knockout of Pi transporter gene and arsenate uptake in Chlamydomonas

Isao Kobayashi1,3, Shoko Fujiwara1, Hiroko Matsumoto1, Sayaka Obata1, Kosuke Shimogawara2, and Mikio Tsuzuki1

1Tokyo University of Pharmacy and Life Sciences, Tokyo, 192-0392 Japan 2Teikyo University School of Medicine, Tokyo, 192-0395 Japan 3Present address: National Institute of Agrobiological Sciences, Ibaraki, 305-8634 Japan

Food production from As-polluted regions is serious problem, and the inhabitants in those regions are suffering from As-related diseases. In recent years, people focus on the removal of pollutants from those regions by plants. To understand As-metabolism and detoxification in plants and algae, we generated As-related mutants of Chlamydomonas reinhardtii by using tagging procedure, and obtained 13 arsenate [As (V)]-resistant and 3 As (V)-sensitive mutants (Fujiwara et al., 2000). In one of As (V)-resistant mutants, AR3, As was accumulated much less than wild type, and putative phosphate (Pi) transporter gene, PTB1, was revealed to have been knocked out by tagging (Kobayashi et al., 2003). As (V) is taken up by algae through Pi transporters. In the genomic database of C. reinhardtii, more than 10 Pi transporter genes (PTA and PTB types) have been identified. Among the products of these genes, PTB1 has a unique, large hydrophilic domain in the middle part of the polypeptide. Phosphorus content in AR3 was twice as high as the wild type due to higher activity of high-affinity Pi transport component. As a result, AR3 suppressed As (V) uptake, but not Pi uptake. These findings suggest that PTB1 is specifically related to As (V) uptake.

e-mail address of presenting author: rj_pink@mac.com