Carboxyl terminal domains of wheat ALMT1 regulate Al activation of the transporter

Abstract

Aluminum ion (Al³⁺) inhibit the root growth in acidic soils. Nevertheless, a variety of plants have a capability to grow in acidic soils by excluding and/or detoxifying the Al³⁺. By the exposure to Al³⁺, a sort of organic acids such as malate or citrate are secreted from the root tips, and the organic acids chelate and detoxify Al³⁺.
Al-resistant cultivars of wheat release malate, which is controlled by the Al-activated malate transporter encoded by the ALMT1 gene. Heterologous expression of the ALMT1 in Xenopus oocytes conferred Al³⁺-activated malate efflux. To clarify the underlying processes for Al³⁺-activated malate efflux via ALMT1, electrophysiological analyses were performed using Xenopus oocytes expressing ALMT1 with desired mutations and truncation in C-terminal domain. Furthermore, Al-activation of chimeric constructs with the C-terminal domain from a homologous ones was analyzed. These results suggested that the three-acidic-amino acids and the whole structure of the C-terminal domain are involved in the Al activation mechanism of ALMT1 protein.