Arabidopsis thaliana - OPUS - Universität Würzburg

Summary
Lipases regulate the biosynthesis of jasmonates. Jasmonates have an essential role
in the development and defense of plants. According to the classical „Vick-
Zimmerman-Pathway“ α-18:3/16:3 released by hydrolases out of galactolipids serve
as substrate for the biosynthesis of jasmonic acid. In the last ten years also the
metabolites of the biosynthesis of jasmonic acid OPDA (derived from α-18:3) and
dnOPDA (derived from 16:3) were found to be esterified in galactolipids of
arabidopsis. The synthesis and function of these complex lipids, named
arabidopsides, is yet not known. An alternative Pathway is postulated in the literature.
According to this the synthesis of dnOPDA/OPDA takes place in galactolipids. Free
dnOPDA/OPDA released by hydrolases may then serve as substrates for the
biosynthesis of jasmonic acid. In the classical „Vick-Zimmerman-Pathway“ as well as
in the alternative Pathway the activity of lipases have an essential impact on the
biosynthesis of jasmonates. Two plastidic acyl-hydrolases with sn1-substrate
specificity, DEFECTIVE IN ANTHER DEHISCENCE1 (DAD1) and DONGLE (DGL),
were published to have a essential role in the biosynthesis of jasmonates in leaves of
Arabidopsis thaliana. DGL should be responsible for the formation of jasmonic acid
under basal conditions and at early timepoints after wounding, DAD1 should maintain
the elevated concentrations of jasmonic acid at later timepoints after wounding.
In this work the involvement of DAD1 in the biosynthesis of OPDA/JA at later
timepoints after wounding was confirmed. However, no differences could be detected
in three independent DGL-RNAi-lines and DAD1-knock-out-mutants in comparison to
the wild type under basal conditions and at early timepoints after wounding which is
contradictory to the published data. In addition, in these mutants wild type oxylipin
levels were found after infection with an avirulent bacterial strain of Pseudomonas
syringae. Furthermore DAD1-deficient mutants displayed dramatic accumulation of
arabidopsides at later timepoints after wounding. Therefore it is suspected that DAD1
is responsible for the release of OPDA esterified in galactolipids. The analysis of
single mutants of 16 additional lipases localised in plastids showed no strong
differences in comparison to the wildtype under basal conditions, after wounding as
well as after infection with P. syringae. Hence, none of the tested lipases plays an
essential role in the biosynthesis of jasmonates. However mutants of the sn1-specific
acyl-hydrolase AtPLA1-Iγ1 (At1g06800) showed significant lower concentrations of
dnOPDA, OPDA and JA after wounding in comparison to the wildtype. This indicates
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