Abstract
Nitrogen deficiency induces senescence and the expression of genes encoding ammonium transporters (AMTs) in terrestrial plants where the AMT family is subdivided into AMT1 and AMT2 subfamilies. Nitrogen starvation in the red seaweed Pyropia yezoensis causes senescence-like discoloration. In this study, we identified five genes in P. yezoensis encoding AMT domain-containing proteins, which were phylogenetically categorized into the AMT1 subfamily. We also found a gene encoding a Rhesus protein (Rh) that was related to, but diverged from, AMTs. Moreover, our phylogenetic analysis showed that AMT domain-containing proteins from micro- and macro-algae belonged to either the AMT1 or Rh subfamily, indicating the absence of AMT2 in algae. Gene expression analyses revealed the presence of gametophyte- and sporophyte-specific AMT1 genes that were up-regulated transiently and continually, respectively, under nitrogen-deficient conditions. In addition, up-regulated sporophyte-specific gene expression was suppressed when nitrogen was resupplied. Accordingly, an expansion of the ancient AMT gene has produced AMT1 functional variants differing in temporal and nitrogen starvation-inducible expression patterns during the life cycle of P. yezoensis. These findings help elucidate the unique nutrition starvation responses involving functionally diverse AMT1 and Rh subfamilies in red seaweed.
Highlights
Expression patterns and physiological roles of ammonium transporters (AMTs) genes have been well studied in animals and land plants [2] [13] [34] [39], algal AMT genes remain poorly understood
We report the presence of the AMT1 and Rhesus protein (Rh) gene subfamilies in P. yezoensis and the diversity in their expression patterns
Our phylogenetic analysis demonstrated the diversity of the AMT1 subfamily, consisting of independent phylum-specific clades (Figure 3)
Summary
Is a major nitrogen source for higher plants and algae [1]. [2] [3] and is used in the biosynthesis of nitrogen-containing compounds such as amino acids and nucleic acids [4] [5]. The influx of extracellular NH4+ into cells is mediated by ammonium transporters (AMTs) [6]. AMTs are encoded by a multigene family comprising the AMT1 and AMT2 subfamilies [2] [7]. AMT1s are responsible for high-affinity NH4+ transport in rice (Oryza sativa), wheat (Triticum aestivum) and many other plant species [5] [7] [8] [9]
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