PARENT SESSION

Symposium S1B Photooxidative stress, photoinhibition
Monday August 30th, 2004 10:20 AM-12:20 PM Room 210A
Chair: Christine Foyer
Co-Chair: Klaus Apel

Oxidative stress networks and nuclear control. Barry Pogson ^*,1, Pip Walter¹, Britta Forster¹, Jan Bart Rossel¹, ¹ School of Biochemistry and Molecular Biology, Canberra, ACT, Australia

ABSTRACT- The key to controlling the suite of antioxidant processes in the cell is a complex set of networks. The components of stress signaling networks for abiotic stresses, such as cold, drought and salt are slowly being identified. But how these processes are regulated under high light and the extent to which different abiotic stresses induce unique or common pathways is not understood. A combination of forward and reverse genetics in Arabidopsis and Chlamydomonas has identified unique sets of mutants and regulatory genes that alter transcriptional and physiological responses to a range of oxidative stresses. Thirteen alx (altered APX expression) mutations were identified by their increased or reduced expression of cytosolic ascorbate peroxidase, APX2, under high light. A number were gain of function. For example, alx8 has a five fold increase in APX2 expression under high light, without any obvious greater tolerance to high light; it is however extremely drought tolerant and has constitutively higher ABA content. Our parallel approach in Chlamydomonas has identified a number of oxidative stress tolerant mutations. With respect to loss of function, a number of mutations and RNAi lines of high light induced genes (identified by microarrays) have one or more of the following: reduced APX2 expression, increased photobleaching, salt sensitivity, chlorosis and reduced capacity to accumulate anthoycanins under stress. The suites of phenotypes demonstrate the interrelationships of abiotic stress signaling networks. Most significantly, they illustrate that the pathways are not simply linear as there are unique combinations of phenotypes in each mutant and transgenic line. Transcript profiling of high light-regulated phosphates, kinesis and transcription factors also demonstrates the pathways are networked and multifaceted, exhibiting negative and positive feedback regulation on each other as well as the downstream genes.

KEY WORDS: oxidative stress, drought, gene networks, high light