Abstract
cDNA for a major arbuscular mycorrhiza (AM)-inducible phosphate (Pi) transporter of Lotus japonicus, LjPT3, was isolated from Glomus mosseae-colonized roots. The LjPT3 transcript was expressed in arbuscule-containing cells of the inner cortex. The transport activity of the gene product was confirmed by the complementation of a yeast mutant. To better understand the physiological role of this AM-inducible Pi transporter, knockdown transformants of the gene were prepared through hairy root transformation and RNA-interference. Under Pi-limiting conditions, the transformants showed a reduction of Pi uptake via AM and growth retardation. The transformants also exhibited a decrease in G. mosseae arbuscules. Additionally, when Mesorhizobium loti was inoculated into the knockdown transformants in combination with G. mosseae, necrotic root nodules were observed. We consider that the genetically engineered host plants had monitored insufficient Pi uptake via AM, excluding the existing fungi and rhizobia and/or preventing further development of the fungal and nodule structures.
