Elucidation of the hrp Clusters of Xanthomonas oryzae pv. oryzicola That Control the Hypersensitive Response in Nonhost Tobacco and Pathogenicity in Susceptible Host Rice

Abstract

Xanthomonas oryzae pv. oryzicola, the cause of bacterial leaf streak in rice, possesses clusters of hrp genes that determine its ability to elicit a hypersensitive response (HR) in nonhost tobacco and pathogenicity in host rice. A 27-kb region of the genome of X. oryzae pv. oryzicola (RS105) was identified and sequenced, revealing 10 hrp, 9 hrc (hrp conserved), and 8 hpa (hrp-associated) genes and 7 regulatory plant-inducible promoter boxes. While the region from hpa2 to hpaB and the hrpF operon resembled the corresponding genes of other xanthomonads, the hpaB-hrpF region incorporated an hrpE3 gene that was not present in X. oryzae pv. oryzae. We found that an hrpF mutant had lost the ability to elicit the HR in tobacco and pathogenicity in adult rice plants but still caused water-soaking symptoms in rice seedlings and that Hpa1 is an HR elicitor in nonhost tobacco whose expression is controlled by an hrp regulator, HrpX. Using an Hrp phenotype complementation test, we identified a small hrp cluster containing the hrpG and hrpX regulatory genes, which is separated from the core hrp cluster. In addition, we identified a gene, prhA (plant-regulated hrp), that played a key role in the Hrp phenotype of X. oryzae pv. oryzicola but was neither in the core hrp cluster nor in the hrp regulatory cluster. A prhA mutant failed to reduce the HR in tobacco and pathogenicity in rice but caused water-soaking symptoms in rice. This is the first report that X. oryzae pv. oryzicola possesses three separate DNA regions for HR induction in nonhost tobacco and pathogenicity in host rice, which will provide a fundamental base to understand pathogenicity determinants of X. oryzae pv. oryzicola compared with those of X. oryzae pv. oryzae.The interaction of many gram-negative plant-pathogenic bacteria with plants is modulated by two sets of genes: the avirulence (avr) or virulence (vir) genes determine host specificity via gene-for-gene interactions, and the hrp genes, which are usually clustered in a chromosomal region that spans 20 to 30 kb, are involved in induction of the hypersensitive response (HR) in resistant host and nonhost plants and pathogenicity in susceptible host plants (2, 7). HR is a rapid, local, programmed cell death that is induced upon recognition of the pathogen and concomitant with the inhibition of pathogen growth within the infected plants. Commonly, the nine hrp genes, which are highly conserved in plant and animal bacterial pathogens, are known as the hrc (hrp conserved) genes (6). The hrc genes encode the type III secretion system (TTSS) and are critical for pathogenicity and initiation of disease (2, 34). Recently, it was established that the hrpF gene in plant-pathogenic bacteria encodes a translocon that is a component of the TTSS (13,31,49). These hrc genes are also found in animal pathogens such as Salmonella and Shigella and are thought to be evolutionarily related to the flagellar apparatus (18,19,20). The hpa (hrpassociated) genes contribute to pathogenicity and to the induction of the HR in nonhost p...

Hpa2 Required by HrpF To Translocate Xanthomonas oryzae Transcriptional Activator-Like Effectors into Rice for Pathogenicity

“…oryzicola (59), and similar gene arrangements are also found in the genomes of X. oryzae pv. oryzae (57), X. campestris pv.…”

“…The expression of hrp genes is induced in planta and in the hrp-inducing medium XOM3 (55) and is controlled by two key regulatory genes, hrpG and hrpX, located outside the hrp gene cluster (59). Commonly, the expression of the hrpA operon and hrpX is activated by an OmpR family member, HrpG (42,54).…”

“…oryzicola, the causative agent of bacterial leaf streak disease in rice, is one of the model organisms for studying the molecular mechanisms of plant-pathogen pathosystems (41,59). The bacterial ability to trigger the hypersensitive response (HR), a rapid and localized programmed cell death in nonhosts or in resistant hosts, and to be pathogenic in host plants depends on a type III secretion system (T3SS) encoded by a 27-kb hrp cluster containing 10 hrp, 9 hrc (hrp-conserved), and 8 hpa (hrp-associated) genes according to the homologous regions in other Xanthomonas species (9,41,59). Some of the hrp-hrc-hpa gene products comprise a pedestal-like T3SS structure that traverses the two bacterial membranes (21,24), a pilus-like secretion channel (HrpE) outside HrcC (52), and a translocon protein (HrpF) in the eukaryotic host membrane (3,4,6,21,48).…”

Elucidation of the Regulon and cis -Acting Regulatory Element of HrpB, the AraC-Type Regulator of a Plant Pathogen-Like Type III Secretion System in Burkholderia pseudomallei

“…However, soaking plantlets in suspensions of nonphytopathogenic P. putida ATCC 12633 or media alone also caused wilting. Moreover, we found that after 36 A hallmark of nearly all plant-pathogenic bacteria is the ability to produce a hypersensitive response in tobacco (13,23,79). Tobacco leaves infiltrated with 10 9 cells ml Ϫ1 of B. thailandensis or P. putida did not elicit a hypersensitive response after 7 days, while those infiltrated with the same amount of R. solanacearum developed a hypersensitive response after 2 days.…”

Ketahanan Beberapa Genotipe Padi Terhadap Penyakit Hawar Daun Bakteri (Xanthomonas Oryzae Pv. Oryzae)

“…Uji hipersensitivitas isolat bakteri terhadap tanaman tembakau dilakukan menurut Zou et al (2006). Koloni hawar daun bakteri hasil isolasi dengan kerapatan ±10 6 sel/ml dalam kultur cair disuntikkan ke tulang daun tanaman tembakau.…”