RESUMO
Rust diseases cause significant reductions annually in yield of cereal crops worldwide. Traditional monoculture cropping systems apply significant selection pressure on the pathogen to cause rapid shifts in pathotypes. Plant breeders strive to stay ahead of the evolving pathogens by releasing new crop genotypes with new rust resistance genes or gene combinations. Owing to the limited number of known resistance genes and the lack of molecular understanding of the plant-pathogen interaction, rusts remain challenging organisms to study, both at organismal and molecular levels. This review discusses recent progress by a number of laboratories towards better understanding the molecular component of rust disease resistance.
Assuntos
Basidiomycota/genética , Basidiomycota/patogenicidade , Grão Comestível/microbiologia , Genoma Fúngico , Basidiomycota/fisiologia , Grão Comestível/genética , Genômica , Imunidade Inata/genética , Mutagênese , Proteômica , Transformação Genética , Fatores de Virulência/genéticaRESUMO
The fungal genus Puccinia contains more than 4,000 species. Puccinia triticina, causal agent of wheat leaf rust, is an economically significant, biotrophic basidiomycete. Little is known about the molecular biology of this group, and tools for understanding gene function have not yet been established. A set of parameters was established for the transient transformation of urediniospores. The expression of three heterologous promoters (actin, elongation factor 1-alpha, and Hss1, Heat Shock 70 protein), derived from Puccinia graminis, was evaluated along with the potential for insertional mutagenesis. The UidA (GUS) gene was used as a marker for transient expression. When transferred into P. triticina urediniospores, transient expression was observed across four helium pressures using one size of gold and three sizes of tungsten microprojectiles. Each of the three promoters displayed strong transient expression in germinated urediniospores; however, higher numbers of GUS-positive urediniospores were observed when either the actin or Hss1 promoters were used. Possible concomitant insertional mutagenesis of several avirulence genes was selected in wheat cultivars harboring the cognate resistance genes. Using a linearized cloning plasmid, stable integration into the genome was achieved as demonstrated by PCR and sequencing analysis.
Assuntos
Basidiomycota/genética , Biolística/métodos , Genoma Fúngico , Mutagênese Insercional/métodos , Transfecção/métodos , Sequência de Bases , Basidiomycota/isolamento & purificação , Biolística/instrumentação , Contagem de Colônia Microbiana , Expressão Gênica , Hélio , Dados de Sequência Molecular , Pressão , Regiões Promotoras GenéticasRESUMO
The diversity of the largest group of plant disease resistance genes, the nucleotide binding site-leucine-rich repeat (NBS-LRR) genes, was examined in cereals following polymerase chain reaction (PCR) cloning and database mining. NBS-LRR genes in rice are a large and diverse class with more than 600 genes, at least three to four times the complement of Arabidopsis. Most occur in small families containing one or a few cross-hybridizing members. Unlike in Arabidopsis and other dicots, the class of NBS-LRR genes coding for a Toll and mammalian interleukin-1 receptor (TIR) domain were not amplified during the evolution of the cereals. Genes coding for TIR domains are present in the rice genome, but have diverged from the NBS-LRR genes. Most cereal genes are similar in structure to the members of the non-TIR class of dicots, although many do not code for a coiled-coil domain in their amino termini. One unique class of cereal genes, with ~50 members, codes for proteins similar to the N-termini and NBS domains of resistance genes but does not code for LRR domains. The resistance gene repertoire of grasses has changed from that of dicots in their independent evolution since the two groups diverged. It is not clear whether this reflects a difference in downstream defense signaling pathways.
Assuntos
Grão Comestível/genética , Genes de Plantas/genética , Variação Genética/genética , Leucina/genética , Nucleotídeos/genética , Nucleotídeos/metabolismo , Proteínas/genética , Sequências Repetitivas de Aminoácidos/genética , Sequência de Aminoácidos , Sítios de Ligação/genética , Sequência Consenso , Sondas de DNA/genética , Dosagem de Genes , Íntrons/genética , Proteínas de Repetições Ricas em Leucina , Dados de Sequência Molecular , Família Multigênica/genética , Fases de Leitura Aberta/genética , Oryza/genética , Filogenia , Doenças das Plantas/genética , Estrutura Terciária de Proteína/genética , Homologia de Sequência do Ácido NucleicoRESUMO
In maize, the Rp3 gene confers resistance to common rust caused by Puccinia sorghi. Flanking marker analysis of rust-susceptible rp3 variants suggested that most of them arose via unequal crossing over, indicating that rp3 is a complex locus like rp1. The PIC13 probe identifies a nucleotide binding site-leucine-rich repeat (NBS-LRR) gene family that maps to the complex. Rp3 variants show losses of PIC13 family members relative to the resistant parents when probed with PIC13, indicating that the Rp3 gene is a member of this family. Gel blots and sequence analysis suggest that at least 9 family members are at the locus in most Rp3-carrying lines and that at least 5 of these are transcribed in the Rp3-A haplotype. The coding regions of 14 family members, isolated from three different Rp3-carrying haplotypes, had DNA sequence identities from 93 to 99%. Partial sequencing of clones of a BAC contig spanning the rp3 locus in the maize inbred line B73 identified five different PIC13 paralogues in a region of approximately 140 kb.