75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

283 GLZ1, a member of family 8 glycosyltransferase, may play a role in programmed cell death
Tsai-Chi Li 1 , John Price 1 , Jyan-Chyun Jang 1, 2
1
Department of Horticulture and Crop Science, The Ohio State University, Columbus, (OH), USA,
2
Department of Plant Cellular and Molecular Biology, The Ohio State University, Columbus, (OH), USA
Programmed cell death (PCD) is a regulated process that is critical for plant survival and development. Localized
cell death can block the spread of the infection during pathogen attack. For certain pathogens, an infection can trigger
oxidative burst and generate reactive oxygen intermediates (ROIs). The ROIs can in turn induce salicylic acid (SA)
accumulation and induce the PCD. The Arabidopsis dwarf mutant glz1 was initially identified as having defects in
development as well as sugar accumulation and translocation (Plant Cell Physiol. 45:1453-1460). GLZ1 encodes a
glycosyltransferase with a sequence highly homologous to Avr9/Cf-9 Rapidly Elicited (ACRE231) protein in tobacco.
The glz1 mutants seem to be tolerant to spontaneous powdery mildew infections, where macroscopic cell death lesions
are not apparent on infected plants. To understand the mechanisms underlying this abnormal response, we conducted
artificial inoculations using fungal pathogens under a controlled environment. Unlike the typical hypersensitive response
seen in wild type plants, in which a few large lesions were found, hundreds of small lesions were formed on glz1 plants.
However, these micro-lesions could neither expand nor effectively prevent the pathogen from spreading to surrounding
healthy tissues. Interestingly, while SA application on wild-type leaves can cause high levels of ROIs accumulation and
cell death, glz1 plants were unaffected by the SA treatment. However, glz1 plants were not completely insensitive to
SA because SA-induced PR1 and PR5 expression appeared to be normal. We hypothesize that the lack of SA-induced
cell death may be due to defects in ROI accumulation and signal transduction. This notion is supported by evidence
indicating that low levels of H 2 O 2 accumulation and compromised cell death (ACD6) gene induction occur when glz1
plants are treated with INA or SA. The glz1 defect appears to have a profound effect on defense and cell death response,
because microarray analyses revealed a trend of down regulation of ACD6, MEK1, RIN4, WAK1, and WRKY70 in the
absence of pathogen infection.
284 The mRNA of a putative Proline-rich Protein is down-regulated during the wounding
response in Arabidopsis
Chenggang Liu, Mona Mehdy
The University of Austin at Austin
Proline-rich Proteins (PRPs), known as glycosylated cell wall structural proteins, have been broadly implicated
in various plant developmental stages and the plant defense response. Some PRPs, which have high tyrosine content,
become insolubilized in the cell wall by wounding or fungal elicitor treatment. In contrast, low tyrosine content PRPs
such as PvPRP1 in French bean are believed to be not involved in this cell wall strengthening process. Previously, our
lab had shown PvPRP1 mRNA was down-regulated through mRNA degradation upon wounding and fungal elicitor
treatment in French bean. Here, we report an Arabidopsis mRNA encoding a putative low tyrosine PRP (AtPRP5)
that is down-regulated by wounding, MeJA and ABA treatment. The mRNA level of AtPRP5 decreased to about 30%
of that in untreated plants in 8 hr. The maximum half-life of AtPRP5 mRNA was estimated to be about 4 hr. Unlike
PvPRP1, nuclear run-on assay showed that the down-regulation of AtPRP5 mRNA upon MeJA treatment was mainly
transcriptional. The luciferase reporter gene fused with the 3’ UTR of AtPRP5 mRNA was stably transferred into plants.
The results indicated that the 3’UTR was not involved in AtPRP5 mRNA stability regulation. Based on Northern blots,
roots and inflorescence have the most abundant mRNA expression level; stem and root have much lower expression
level. Transgenic plants with a promoter-GUS fusion indicated that AtPRP5 gene was transcriptionally active in the
vascular bundle region throughout the plants. The mutant plants with a transposon insertion in AtPRP5 gene did not
show any difference from wild type plants under normal growth conditions. However, the seeds of this mutant showed
significant insensitivity to ABA inhibition during seed germination. Together, these results suggest that AtPRP5 plays a
specific role in plant development.