title: Identification of duplicated and stress-inducible Aox2b gene co-expressed with Aox1 in species of the Medicago genus reveals a regulation linked to gene rearrangement in leguminous genomes.
abstract: In flowering plants, alternative oxidase (Aox) is encoded by 3-5 genes distributed in 2 subfamilies (Aox1 and Aox2). In several species only Aox1 is reported as a stress-responsive gene, but in the leguminous Vigna unguiculata Aox2b is also induced by stress. In this work we investigated the Aox genes from two leguminous species of the Medicago genus (Medicago sativa and Medicago truncatula) which present one Aox1, one Aox2a and an Aox2b duplication (named here Aox2b1 and Aox2b2). Expression analyses by semi-quantitative RT-PCR in M. sativa revealed that Aox1, Aox2b1 and Aox2b2 transcripts increased during seed germination. Similar analyses in leaves and roots under different treatments (SA, PEG, H2O2 and cysteine) revealed that these genes are also induced by stress, but with peculiar spatio-temporal differences. Aox1 and Aox2b1 showed basal levels of expression under control conditions and were induced by stress in leaves and roots. Aox2b2 presented a dual behavior, i.e., it was expressed only under stress conditions in leaves, and showed basal expression levels in roots that were induced by stress. Moreover, Aox2a was expressed at higher levels in leaves and during seed germination than in roots and appeared to be not responsive to stress. The Aox expression profiles obtained from a M. truncatula microarray dataset also revealed a stress-induced co-expression of Aox1, Aox2b1 and Aox2b2 in leaves and roots. These results reinforce the stress-inducible co-expression of Aox1/Aox2b in some leguminous plants. Comparative genomic analysis indicates that this regulation is linked to Aox1/Aox2b proximity in the genome as a result of the gene rearrangement that occurred in some leguminous plants during evolution. The differential expression of Aox2b1/2b2 suggests that a second gene has been originated by recent gene duplication with neofunctionalization.
authors.affiliation: Department of Biochemistry and Molecular Biology, Federal University of Ceara, 60455-760 Fortaleza, Ceará, Brazil.
authors.forename: João Henrique Frota
authors.initials: JH
authors.lastname: Cavalcanti
authors.forename: Georgia Mesquita
authors.initials: GM
authors.lastname: Oliveira
authors.forename: Kátia Daniella da Cruz
authors.initials: KD
authors.lastname: Saraiva
authors.forename: José Pedro Pires
authors.initials: JP
authors.lastname: Torquato
authors.forename: Ivan G
authors.initials: IG
authors.lastname: Maia
authors.forename: Dirce Fernandes
authors.initials: DF
authors.lastname: de Melo
authors.forename: José Hélio
authors.initials: JH
authors.lastname: Costa
mesh_terms: D032461:Chromosomes, Plant / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D015321:Gene Rearrangement / Q000235:genetics*; D020131:Genes, Duplicate / Q000235:genetics*; D017343:Genes, Plant / Q000235:genetics; D018745:Genome, Plant / Q000235:genetics*; D018525:Germination / Q000235:genetics; D029902:Medicago / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics*; D000099188:Alternative Oxidase
chemical_list: D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger; D000099188:Alternative Oxidase
keywords: 1-naphthaleneacetic acid; Alfalfa; Alternative oxidase; Aox; Aox2b duplication; Chr; DNA complementary to RNA; H(2)O(2); LEA proteins; Late Embryogenesis Abundant proteins; NAA; PEG; ROS; SA; TCA; TSS; alternative oxidase; cDNA; chromosome; polyethylene glycol; reactive oxygen species; salicylic acid; transcriptional start site; tricarboxylic acid