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Biomedical subjects

Jan E Leach

Publications and source records attributed to Jan E Leach.

7 recordsLinked to original sources
PubMed2006

Suppression of defense response in plants by the avrBs3/pthA gene family of Xanthomonas spp.

Effector genes of some plant-pathogenic bacteria, including some members of the avrBs3/pthA effector gene family from Xanthomonas spp., confer not only genotype-specific disease resistance but also pathogen aggressiveness or virulence. In addition, some effector gene products suppress induction of a nonspecific (or general) hypersensitive response (HR). To determine whether the Xanthomonas avrBs3/pthA gene family members apl1, avrXa7, or avrXa10 also confer suppressor activity, we introduced constructs with each effector gene into Pseudomonas fluorescens 55 that expressed the entire hrp cluster from P. syringae pv. syringae in cosmid pHIR11. When inoculated to tobacco 'Bright Yellow', P fluorescens (pHIR11) induces the HR and expression of four tobacco defense response genes: HIN1, RbohB, PAL, and PR1. When P. fluorescens double transformants that contained pHIR11 and constructs with apl1, avrXa7, or avrXa10 were infiltrated into tobacco, the HR and expression of three defense response genes, RbohB, PAL, and PR1, were suppressed. The suppression of the HR and defense gene expression was more efficient in the transformants with the apl1 and avrXa7 than the transformant with avrXa10. Although expression of other defense genes was suppressed by the double transformants, HIN1 expression was the same level as was observed after infiltration with P. fluorescens (pHIR11), suggesting that HIN1 may not be involved directly in HR. Taken together, our data suggest that avrXa7, avrXa10, and apl1, when delivered to plant cells by the P. syringae pv. syringae hrp secretion system, can suppress nonhost HR and associated phenotypes.

Bacterial Proteins↗
PubMed2004

The avrRxo1 gene from the rice pathogen Xanthomonas oryzae pv. oryzicola confers a nonhost defense reaction on maize with resistance gene Rxo1.

Maize lines that contain the single dominant gene Rxo1 exhibit a rapid hypersensitive response (HR) after infiltration with the rice bacterial streak pathogen Xanthomonas oryzae pv. oryzicola, but not with the rice bacterial blight pathogen X. oryzae pv. oryzae. The avirulence effector gene that corresponds to Rxo1, designated avrRxo1, was identified in an X. oryzae pv. oryzicola genomic library. When introduced into X. oryzae pv. oryzae, clones containing avrRxo1 induced an HR on maize with Rxo1, but not on maize without Rxo1. The avrRxo1 gene is 1,266 bp long and shows no significant homology to any database sequences. When expressed in an X. oryzae pv. oryzae hrpC mutant that is deficient in the type III secretion system, avrRxo1 did not elicit the HR, indicating that the avrRxo1-Rxo1 interaction is dependent on type III secretion. Transient expression of avrRxo1 in onion cells after biolistic delivery revealed that the protein product was associated with the plasma membrane. Transient expression in maize lines carrying Rxo1 resulted in cell death, suggesting that AvrRxo1 functions from inside maize cells to elicit Rxo1-dependent pathogen recognition.

Amino Acid Sequence↗
PubMed2004

[Cellular responses of rice to Magnaporthe grisea at the early stages of disease development].

This paper presents a detailed investigation of the cytological and cytochemical events in rice cells infected by Magnaporthe grisea during the early stages of disease development. It was demonstrated that the spatial and temporal development of cytoplasmic aggregation, host cell autofluorescence, callose deposition and phospholipase D (PLD) accumulation were some of the earliest responses of host cells to M. grisea attacking and showed different patterns between the compatible and incompatible interaction. In the cv. IR64 and strain BN111 interaction (resistant), the earliest cellular response observed in the inner epidermis of rice leaf sheath was aggregation of the cytoplasm. Then, the attacked host cells turned brown and the cell cytoplasm collapsed (HR). In the moderately resistant reactions of cv. IR64 to strain PO66, the granule formation was delayed, and no apposition was observed in host cells. In the compatible reactions of cv. IR64 to strain Ca89, no visible cellular response was detected until 40 h after inoculation. As to auto-fluorescence of host cells, some penetration sites showed faint fluorescence under blue light as early as 12 h after inoculation in the cv. IR64-strain BN111 interaction. As the disease developed, the percentage of attacked epidermal cells showing autofluorescence increased quickly from 20 to 24 h after inoculation and the penetrated host cells showed strong autofluorescence. In the moderately resistant interaction, autofluorescence had been detected until 24 h after inoculation. In the compatible interaction, little autofluorescent cell was detected during the disease development. Patterns of callose deposition and phospholipase Dgamma (PLDgamma) showed the similar dynamic characteristics as did the phenolic compounds.

Cytoplasm↗
PubMed2003

Rice phospholipase D isoforms show differential cellular location and gene induction.

Phospholipase D (PLD) has emerged as an important enzyme involved in signal transduction, stress responses, protein trafficking, and membrane metabolism. This report describes the cloning and characterization of three novel PLD genes from rice, designated RPLD3, RPLD4 and RPLD5. The rice PLDs, including the previously isolated RPLD1 and RPLD2, are similar to PLD subfamilies of Arabidopsis: Based on sequence homology and domain conservation, RPLD1 is most similar to the PLDalpha subfamily of PLDs while RPLD5 most closely resembles the PLDdelta type. RPLD2, 3 and 4 represent a unique subfamily, although they are most similar to PLDalpha. RPLD1 is located on chromosome 1, RPLD5 on chromosome 3, and RPLD2, RPLD3, and RPLD4 are tandemly arrayed on chromosome 5. Transcriptional analysis reveals that RPLD1, present in healthy rice vegetative tissues, is induced rapidly but transiently in wounded leaf tissues. RPLD2, also induced by wounding, is present at lower levels but for a more prolonged duration than RPLD1. Immunolocalization with peptide specific antibodies to each of the five PLDs was used to demonstrate that the isoforms have overlapping but distinct patterns of distribution in healthy rice cells. RPLD1 was detected in mesophyll cell wall, membranes, and chloroplasts, whereas RPLD3 and RPLD4 were located predominantly in the chloroplasts. Labeling of RPLD2 and RPLD5 was sparse, and was most concentrated in the secondary walls of xylem (RPLD2) and guard cells (RPLD2 and RPLD5). This combined information on structural features, expression profiles, and cellular localization will assist the basis for dissection of PLD isoform function in rice.

Amino Acid Sequence↗
PubMed2002

Diversity in nucleotide binding site-leucine-rich repeat genes in cereals.

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.

Amino Acid Sequence↗