Recent Progress in Elucidating the Structure, Function and Evolution of Disease Resistance Genes in Plants

Plants employ multifaceted mechanisms to fight with numerous pathogens in nature. Resistance （R） genes are the most effective weapons against pathogen invasion since they can specifically recognize the corresponding pathogen effectors or associated protein（s） to activate plant immune responses at the site of infection. Up to date, over 70 R genes have been isolated from various plant species. Most R proteins contain conserved motifs such as nucleotide-binding site （NBS）, leucine-rich repeat （LRR）, Toll-interleukin-1 receptor domain （TIR, homologous to cytoplasmic domains of the Drosophila Toll protein and the manamalian intefleukin-1 receptor）, coiled-coil （CC） or leucine zipper （LZ） structure and protein kinase domain （PK）. Recent results indicate that these domains play significant roles in R protein interactions with effector proteins from pathogens and in activating signal transduction pathways involved in innate immunity. This review highlights an overview of the recent progress in elucidating the structure, function and evolution of the isolated R genes in different plant-pathogen interaction systems.

Quantitative Structure-property Relationship Studies on Amino Acid Conjugates of Jasmonic Acid as Defense Signaling Molecules

Jasmonates and related compounds, including amino acid conjugates of jasmonic acid, have regulatory functions in the signaling pathway for plant developmental processes and responses to the complex equilibrium of biotic and abiotic stress. But the molecular details of the signaling mechanism are still poorly understood. Statistically significant quantitative structure-property relationship models （r^2 〉 0.990） constructed by genetic function approximation and molecular field analysis were generated for the purpose of deriving structural requirements for lipophilicity of amino acid conjugates of jasmonic acid. The best models derived in the present study provide some valuable academic information in terms of the 2/3D-descriptors influencing the lipophilicity, which may contribute to further understanding the mechanism of exogenous application ofjasmonates in their signaling pathway and designing novel analogs of jasmonic acid as ecological pesticides.

Suppression of edr2-mediated powdery mildew resistance, cell death and ethylene-induced senescence by mutations in ALD1 in Arabidopsis

EDR2 is a negative regulator of the defense response and cell death in Arabidopsis.Loss-of-function of EDR2 leads to enhanced resistance to powdery mildew.To identify new components in the EDR2 signal transduction pathway,mutations that suppress edr2 resistant phenotypes were screened.Three mutants,edts5-1,edts5-2 and edts5-3（edr two suppressor 5）,were identified.The EDTS5 gene was identified by map-based cloning and previously was shown to encode an aminotransferase（ALD1）.Therefore we renamed these three alleles ald1-10,ald1-11 and ald1-12,respectively.Mutations in ALD1 suppressed all edr2-mediated phenotypes,including powdery mildew resistance,programmed cell death and ethylene-induced senescence.Accumulation of hydrogen peroxide in edr2 was also suppressed by ald1 mutation.The expression of defense-related genes was up-regulated in the edr2 mutant,and the up-regulation of those genes in edr2 was suppressed in the edr2/ald1 double mutant.The ald1 single mutant displayed delayed ethylene-induced senescence.In addition,ald1 mutation suppressed edr1-mediated powdery mildew resistance,but could not suppress the edr11edr2 double-mutant phenotype.These data demonstrate that ALD1 plays important roles in edr2-mediated defense responses and senescence,and revealed a crosstalk between ethylene and salicylic acid signaling mediated by ALD1 and EDR2.