Production of disease symptoms represents the final phase of infectious diseases and is a main cause of crop loss and/or marketability. However, little is known about the molecular basis of disease symptom development. In this study, a genetic screening was conducted to identify Arabidopsis (Arabidopsis thaliana) mutants that are impaired specifically in the development of disease symptoms (leaf chlorosis and/or necrosis) after infection with the bacterial pathogen Pseudomonas syringae pv tomato (Pst) DC3000. An ethyl methanesulfonate-induced Arabidopsis mutant (no chlorosis1 [noc1]) was identified. In wild-type plants, the abundance of chlorophylls decreased markedly after Pst DC3000 infection, whereas the total amount of chlorophylls remained relatively unchanged in the noc1 mutant. Interestingly, noc1 mutant plants also exhibited reduced disease symptoms in response to the fungal pathogen Alternaria brassicicola. Genetic and molecular analyses showed that the nuclear gene STAYGREEN (SGR; or Mendel's I locus) is mutated (resulting in the aspartic acid to tyrosine substitution at amino acid position 88) in noc1 plants. Transforming wild-type SGR cDNA into the noc1 mutant rescued the chlorosis phenotype in response to Pst DC3000 infection. The SGR transcript was highly induced by Pst DC3000, A. brassicicola, or coronatine (COR), a bacterial phytotoxin that promotes chlorosis. The induction of SGR expression by COR is dependent on COI1, a principal component of the jasmonate receptor complex. These results suggest that pathogen/COR-induced expression of SGR is a critical step underlying the development of plant disease chlorosis.
Alternaria/pathogenicity , Arabidopsis Proteins/genetics , Arabidopsis/genetics , Plant Diseases/immunology , Pseudomonas syringae/pathogenicity , Amino Acid Sequence , Amino Acids/metabolism , Arabidopsis/immunology , Arabidopsis/microbiology , Arabidopsis Proteins/metabolism , Chromosome Mapping , Cyclopentanes/metabolism , DNA, Complementary/genetics , Gene Expression Regulation, Plant , Genetic Complementation Test , Genetic Loci , Indenes/metabolism , Molecular Sequence Data , Mutation , Oxylipins/metabolism , Phenotype , Plant Diseases/microbiology , Plant Growth Regulators/metabolism , Plant Leaves/genetics , Plant Leaves/immunology , Plant Leaves/microbiology , Sequence Alignment , Sequence Analysis, DNA , Virulence
A phylogeny of the genus Montanoa based on the internal transcribed spacer (ITS) and the external transcribed spacer (ETS) is presented. Each of the two clades revealed by the Bayesian and parsimony analyses has approximately half of the number of species in the genus. One lineage is composed mostly of central and southern Mexican species whereas the other lineage contains those species endemic to Mesoamerica and South America. The molecular phylogeny is compared to previous phylogenetic hypotheses based on morphological characters. Key features in the structure of the capitulum such as pale morphology, heavily used in the past to construct hypotheses of relationship within the genus, are viewed as of minimal value to circumscribe natural groups. The relationships of Montanoa to other genera in the Heliantheae are briefly discussed.
Asteraceae/genetics , DNA, Intergenic/genetics , DNA, Plant , Genes, Plant , Montanoa/genetics , Genetic Variation , Phylogeny , Species Specificity
