Ammonium transporter genes in millets: insights into structure, function, evolutionary conservation, divergence, and phylogenetic analysis

Millets, resilient and nutritionally rich crops, are increasingly recognized for their potential in sustainable agriculture. Ammonium transporter (AMTs) gene family significantly contribute to the absorption and transport of NH₄⁺ form of nitrogen in plants. The information about the structure and function of ammonium transporter genes in millet species is lacking. The millet crops such as pearl millet, proso millet, finger millet, sorghum, foxtail millet and green foxtail millet exhibit genetic variation in AMTs, which can be harnessed to improve NUE. Thus, genomic sequences of the six millet species were used and a total of 53 AMT genes were identified. Further, comprehensive analysis of chromosomal distribution, transmembrane structure prediction, presence of exons and introns, domain and motif organization, phylogeny, and synteny analysis were carried out. The phylogenetic analysis illustrated that millet AMTs belong to two subfamilies AMT1 and AMT2 (AMT2/AMT3/AMT4). Ka/Ks analysis showed that segmental duplications have contributed considerably in the evolution of millet AMTs. Phylogenetic classification of members of Poaceae using the amino acid sequences of AMT1.1 genes confirms the speciation patterns shown by matK gene sequence. Promoter analysis of millet AMTs showed presence of cis-elements related to light response, anaerobic induction, growth hormones, drought stress, biotic stress and several endogenous signals related to plant growth and development. This research provides insights into the structural and functional aspects of ammonium transporter genes in millets, and will serve as a foundation for utilizing AMTs for devising NUE strategies.

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