Tyrosine phosphatase signalling in a lower plant: cell‐cycle and oxidative stress‐regulated expression of the Chlamydomonas eugametos VH‐PTP13 gene

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Abstract
The first evidence for tyrosine phosphatase signalling pathways in plants is presented by characterizing a putative protein tyrosine phosphatase gene from the unicellular green alga Chlamydomonas eugametos. This cDNA, referred to as VH‐PTP13, contains an open reading frame specifying a protein with a molecular weight of 30.3 kDa, that has significant homology with a distinct group of dual‐specificity phosphatases. The highest homology is found with CL‐100, a human stress‐response gene that regulates MAPkinase activity. The purified VH‐PTP13 protein expressed in E. coli had phosphatase activity and inactivated MAPkinases from alfalfa and tobacco. Non‐dividing C. eugametos gametes did not express the VH‐PTP13 gene whereas synchronously dividing vegetative cells only expressed VH‐PTP13 in the early G1‐phase of the cycle, implying a function there. When vegetative cells were subjected to oxidative stress, expression of the VH‐PTP13 gene was strongly induced, analogous to the human CL‐100 gene. Its potential role in plant signalling pathways is discussed.

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