The iron and manganese transporter AtNRAMP5 contributes to male fertility in Arabidopsis thaliana
Résumé
One of the currently best-established relationships between male fertility and resources at the plant scale highlights the importance of transition metals. The NRAMP gene family encodes proteins mediating the transport of a wide range of transition metals in prokaryotic and eukaryotic cells. Here, we identified AtNRAMP5 as a major contributor to male fertility. Expression in yeast shows that AtNRAMP5 complements the growth defect of smf2 mutant, which is impaired in intracellular Mn2+ trafficking. AtNRAMP5 expression also leads to a strong increase in yeast manganese and iron concentrations.
AtNRAMP5 is highly and specifically expressed in pollen and AtNRAMP5 ectopic expression in Arabidopsis thaliana vegetative tissues is deleterious. During the last stages of pollen development, AtNRAMP5 is suddenly activated and becomes one of the 3% highest expressed loci. In vivo competition between a wildtype and a disrupted allele of AtNRAMP5 shows a significant segregation bias towards the wild type allele. Expression of AtNRAMP5 fused to GFP under its own promoter restores normal transmission. Microscopic observation shows that AtNRAMP5-GFP is localized in intracellular compartments of mature pollen and pollen tubes. Perls/DAB staining reveals that iron is concentrated in intracellular compartments in wild-type mature pollen, whereas this pattern of iron staining is disrupted in nramp5 mutant. All together, our results provide insights into the role of transition metals during an important step of the life cycle through the action of a highly expressed transporter.