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

425 Characterization of an intragenic suppressor of bri1-5
Michael Wierzba 1 , Rene Michel 1 , Amanda Durbak 1 , Robert Schmitz 2 , Andrea Aguirre 1 , Scott Rowe 3 , Shozo Fujioka 4 ,
Frans Tax 1
1
University of Arizona, Tucson, AZ, 2 University of Wisconsin, Madison, WI, 3 Washington University, St. Louis,
MO, 4 RIKEN, Japan
The receptor-like kinase (RLK) Brassinosteroid Insenstive-1 (BRI1) is the major receptor for steroid hormones in
Arabidopsis. Null mutants in BRI1 are dwarfed and display a reduction in the length of leaves, petioles, pedicels and
internodes. Using the weak allele bri1-5, we isolated a dominant suppressor of its dwarf phenotype. The results of genetic
and molecular tests indicated that the suppression was caused by a second site mutation in BRI1 that we named bri1-11.
A thorough characterization of bri1-5 bri1-11 and bri1-5 phenotypes revealed that in most tissues, bri1-5 bri1-11 plants
were intermediate between bri1-5 and wild type in size and in their response to BRs. These results suggested that the
bri1-11 mutation partially restored the function of bri1-5. To understand the mechanism through which the bri1-5 bri1-
11 receptor works, we manipulated the activity of ligand, the BRI1 interacting RLK BAK1, and the downstream kinase
BIN2. Here we report these results as well as additional characterization.
426 Characterisation of New Regulators in ROS-Induced Cell Death
Michael Wrzaczek 1 , Mikael Brosche 1 , Hannes Kollist 1, 2 , Triin Kollist 1, 2 , Jaakko Kangasjarvi 1
1
Plant Biology, Department of Biological and Environmental Sciences, Viikki Biocenter, University of Helsinki,
POB 65 (Viikinkaari 1), 00014 Helsinki, Finland, 2 Institute of Molecular and Cell biology, University of Tartu,
Riia str. 23, Tartu, Estonia
Initially considered primarily as toxic compounds reactive oxygen species (ROS) are accepted to play a more
complicated role. ROS appear to be ubiquitously used as signaling compounds that are produced in response to many
biotic and abiotic stresses, including short and high pulses of the atmospheric pollutant ozone (O 3 ) and pathogen infection.
The formation of ROS in the apoplastic space of leaves triggers hypersensitive response-like programmed cell death
(PDC) lesions in the leaves of sensitive plants. This is a common feature of plant responses to ozone and pathogens and
appears to be an active process during which ROS exhibit signaling functions in inter- and intracellular communication.
While central components to pathogen recognition and signaling have been identified, the key elements in ROS perception
as well as the regulators of lesion spread and lesion containment remain elusive. Receptor-like kinases (RLKs) exhibit
important functions in the sensing of pathogens and developmental cues. Subsequently signaling networks are triggered
including phosphorylation and de-phosphorylation events that lead to the adjustment of gene expression. Ultimately this
leads to a co-ordinated and fine-tuned defense response. Taken together it is conceivable that ROS are perceived and
processed in a similar way to pathogens, potentially sharing several signaling components.
Genes were selected for early transcriptional upregulation upon O 3 exposure. A screen for O 3 sensitivity in the
corresponding knockouts identified several signaling components including amongst others components in calcium
signaling, a putative lipase, various proteins of unknown function and two RLKs. Obtained data suggests the involvement
of phosphorylation cascades in ROS signaling. Furthermore, the small extracellular proteins as well as RLKs might be
directly involved in the regulation of O 3 -induced lesion formation and possibly ROS perception. The study of the biological
function and the biochemical properties of the identified proteins will allow for new insights into ROS perception and
early ROS signaling. Furthermore these results will help to understand the role of ROS signaling in other biotic and
abiotic stresses.