The family of ammonium transporters ( AMT ) in S orghum bicolor : two AMT members are induced locally, but not systemically in roots colonized by arbuscular mycorrhizal fungi

Summary Arbuscular mycorrhizal ( AM ) fungi contribute to plant nitrogen (N) acquisition. Recent studies demonstrated the transport of N in the form of ammonium during AM symbiosis. Here, we hypothesize that induction of specific ammonium transporter ( AMT ) genes in S orghum bicolor during AM colonization might play a key role in the functionality of the symbiosis. For the first time, combining a split‐root experiment and microdissection technology, we were able to assess the precise expression pattern of two AM ‐inducible AMT s, Sb AMT 3;1 and Sb AMT 4 . Immunolocalization was used to localize the protein of Sb AMT 3;1 . The expression of Sb AMT 3;1 and Sb AMT 4 was greatly induced locally in root cells containing arbuscules and in adjacent cells. However, a split‐root experiment revealed that this induction was not systemic. By contrast, a strictly AM ‐induced phosphate transporter ( SbPt11 ) was expressed systemically in the split‐root experiment. However, a gradient of expression was apparent. Immunolocalization analyses demonstrated that Sb AMT 3;1 was present only in cells containing developing arbuscules. Our results show that the Sb AMT 3;1 and Sb AMT 4 genes are expressed in root cortical cells, which makes them ready to accommodate arbuscules, a process of considerable importance in view of the short life span of arbuscules. Additionally, Sb AMT 3;1 might play an important role in N transfer during AM symbiosis.