Three types of defense-responsive genes are involved in resistance to bacterial blight and fungal blast diseases in rice

Bacterial blight and fungal blast diseases of rice, caused by Xanthomonas oryzae pv. oryzae and Pyricularia grisea Sacc., respectively, are two of the most devastating diseases in rice worldwide. To study the defense responses to infection with each of these pathogens, expression profiling of 12 defense-responsive genes was performed using near-isogenic rice lines that are resistant or susceptible to bacterial blight and fungal blast, respectively, and rice cultivars that are resistant or susceptible to both pathogens. All 12 genes showed constitutive expression, but expression levels increased in response to infection. Based on their expression patterns in 12 host-pathogen combinations, these genes could be classified into three types, pathogen non-specific (6), pathogen specific but race non-specific (4) and race specific (2). Most of the 12 genes were only responsive during incompatible interactions. These results suggest that bacterial blight and fungal blast resistances share common pathway(s), but are also regulated by different defense pathways in rice. Activation of the corresponding R gene is the key step that initiates the action of these genes in defense responses. The chromosomal locations and pathogen specificities of seven of the 12 genes were consistent with those of previously identified quantitative trait loci for rice disease resistance, which indicates that some of the 12 genes studied may have a phenotypic impact on disease resistance in rice.     

Insect feeding-induced differential expression of <Emphasis Type="Italic">Beta vulgaris</Emphasis> root genes and their regulation by defense-associated signals

Root responses to insect pests are an area of plant defense research that lacks much information. We have identified more than 150 sugar beet root ESTs enriched for genes responding to sugar beet root maggot feeding from both moderately resistant, F1016, and susceptible, F1010, genotypes using suppressive subtractive hybridization. The largest number of identified F1016 genes grouped into the defense/stress response (28%) and secondary metabolism (10%) categories with a polyphenol oxidase gene, from F1016, identified most often from the subtractive libraries. The differential expression of the root ESTs was confirmed with RT-PCR. The ESTs were further characterized using macroarray-generated expression profiles from F1016 sugar beet roots following mechanical wounding and treatment of roots with the signaling molecules methyl jasmonate, salicylic acid and ethylene. Of the examined root ESTs, 20, 17 and 11% were regulated by methyl jasmonate, salicylic acid and ethylene, respectively, suggesting these signaling pathways are involved in sugar beet root defense responses to insects. Identification of these sugar beet root ESTs provides knowledge in the field of plant root defense and will lead to the development of novel control strategies for control of the sugar beet root maggot.Electronic Supplementary Material Supplementary material is available in the online version of this article at and is accessible for authorized users     

Construction of suppression subtractive hybridization libraries and identification of brown planthopper-induced genes

A suppression subtractive hybridization technique was used to screen for brown planthopper (BPH)-inducible genes in rice (Oryza sativa). cDNAs from a BPH-resistant rice line (B5) infested by BPH were used as the tester population, and mixed cDNAs from a BPH-sensitive line (MH63) and a control (uninfested B5) as the driver population. After hybridizing and cloning, forward and reverse subtraction cDNA libraries were obtained, containing 5700 clones. These clones were further analyzed by differential gene expression screening, and 154 clones that were clearly induced by BPH were identified. Sequencing analysis and homology searching showed that these clones represent 136 single genes, which were assigned to functional categories, including 10 putative cellular functions, according to categories established for Arabidopsis. The 136 genes include 21 known to be related to disease, wound and other stresses, most of which were found to be up-regulated in BPH feeding responses. In addition, an Oryza cysteine inhibitor and a beta-glucosidase belonging to the 21 genes group were found in the rice response to BPH feeding, these two genes have previously been shown to be induced in plant responses to chewing insects. Our results not only confirm that several identical genes are activated in defense mechanisms against both sucking and chewing insects, but also show that genes have overlapping functions in both pathogen and insect resistance.     

Gene suppression in a tolerant tomato–vascular pathogen interaction

A plant can respond to the threat of a pathogen through resistance defenses or through tolerance. Resistance has been widely studied in many host pathogen systems but little is known about genetic changes which underlie a tolerant interaction. A recently developed model system for a tolerant tomato (Lycopersicon esculentum Mill) interaction with a fungal wilt pathogen, Verticillium dahliae Kleb, is examined with respect to changes in gene expression and compared to a susceptible infection. The results indicate that genetic changes can be dramatically different and some genes that are strongly elevated in the susceptible interaction are actually down-regulated in tolerance. Similar levels of fungal DNA and an up-regulation of many pathogenesis related genes indicate that in both types of interaction the presence of fungus is clearly recognized by the plant but other changes correlate with the absence of symptoms in the tolerant interaction. For example, a gene encoding a known 14-3-3 regulatory protein and a number of genes normally affected by this protein are down-regulated. Furthermore, genes which may contribute to foliar necrosis and cell death in the susceptible interaction also appear to be suppressed in the tolerant interaction, raising the possibility that the wilt symptoms, chlorosis and necrosis which are observed in the susceptible interaction, are actually programmed to further limit the growth of the fungal pathogen, and protect the general tomato population.