TYROSINE PHOSPHATASE SIGNALING IN A LOWER PLANT - CELL-CYCLE AND OXIDATIVE STRESS-REGULATED EXPRESSION OF THE CHLAMYDOMONAS-EUGAMETOS VH-PTP13 GENE

The first evidence for tyrosine phosphatase signalling pathways in pla nts is presented by characterizing a putative protein tyrosine phospha tase gene from the unicellular green alga Chlamydomonas eugametos. Thi s cDNA, referred to as VH-PTP13, contains an open reading frame specif ying a protein with a molecular weight of 30.3 kDa, that has significa nt homology with a distinct group of dual-specificity phosphatases. Th e highest homology is found with CL-100, a human stress-response gene that regulates MAPkinase activity. The purified VH-PTP13 protein expre ssed in E. coli had phosphatase activity and inactivated MAPkinases fr om alfalfa and tobacco. Nondividing C. eugametos gametes did not expre ss the VH-PTP13 gene whereas synchronously dividing vegetative cells o nly expressed VH-PTP13 in the early G1-phase of the cycle, implying a function there. When vegetative cells were subjected to oxidative stre ss, expression of the VH-PTP13 gene was strongly induced, analogous to the human CL-100 gene. Its potential role in plant signalling pathway s is discussed.