15th International Conference on Arabidopsis Research - TAIR

T05-003
Understanding the molecular mechanisms of the
glucosinolate-myrosinase system in plant-aphid
interactions
Carina Barth(1), Georg Jander(1)
1-Boyce Thompson Institute for Plant Research, Ithaca, NY 14853, USA
Plants have evolved a variety of mechanisms including physical and chemical
barriers (repellents, toxins) to protect themselves from herbivory. In Arabidopsis
and other crucifers, the glucosinolate-myrosinase system acts as a chemical
defense against herbivore attack. Glucosinolates, a class of thioglucosides,
and the enzyme myrosinase (b-thioglucoside glucohydrolase, TGG) are
compartmentalized in different plant cells. Tissue disruption, e.g. wounding
caused by insect herbivores, allows myrosinase to cleave glucosinolates and
results in the release of toxic products such as isothiocyanates, nitriles and
thiocyanates. Although glucosinolate breakdown products repel most insects,
they are also involved in host plant recognition by some crucifer-feeding
specialist herbivores.
The goal of this work is to understand the role of the Arabidopsis
myrosinase enzyme in glucosinolate turnover and insect defense. T-DNA
insertion lines with defects in TGG1 and TGG2, the two known functional
myrosinase genes in Arabidopsis, are being studied. Complete knockout
mutations of the respective TGG genes were verified by RT-PCR. The mutants
do not differ morphologically from the wild-type plants. However, at different
developmental stages and in various tissues, myrosinase activity, determined
spectrophotometrically as degradation of the glucosinolate sinigrin, is
approximately 5% of wild-type activity in tgg1 mutants, but is not significantly
different from wild type in tgg2 mutants. Initial analysis of the glucosinolate
content of tgg mutants showed no significant quantitative or qualitative
changes from wild-type levels.
The mutant lines were investigated to determine whether altered
myrosinase activity is involved in defense against the generalist herbivore
Myzus persicae (green peach aphid) and the specialist herbivore Brevicoryne
brassicae (cabbage aphid). Reproduction of M. persicae was not significantly
different on wild type and mutant plants. In contrast, the specialist B. brassicae
reproduced two to three times better on the tgg1 mutants than on the
wild type and the tgg2 mutant plants. Feeding strategies and the role of the
glucosinolate-myrosinase system in defense responses to M. persicae and B.
brassicae will be discussed.
T05 Interaction with the Environment 2 (Biotic)
T05-004
DETERMINATION IN ARABIDOPSIS THALIANA OF
PGPR EFFECT, ISR ACTIVITY AND THE POSSIBLE ISR-
RESPONDING-WAY IN HIZOBACTERIAS ISOLATED
FROM THE ROOTS OF NICOTIANA GLAUCA.
Domenech, J.(1)
1-Universidad San Pablo CEU
Domenech, J., Pereyra, T., Barriuso, J., Ramos, B. and Gutiérrez-Mañero, J.
Universidad San Pablo CEU. Ctra. Boadilla km. 5,3. Boadilla del Monte.
28668 Madrid.
According to experiments made before with 56 strains of Nicotiana glauca,
which include siderophore production, chitinolytic activity and PGPR effect
on tomato, (in preparation), six rhizobacteria were selected: N5.18, N6.8,
N11.37, N17.35, N19.27, N21.4. In these work PGPR effect will be tested
on Arabidopsis thaliana Col-0. On the other hand, ISR bioassays were also
carried out to determine if these PGPR strains, induce protection against the
pathogen Xanthomonas campestris CECT 95. Finally, the strains that induces
systemic resistance were tested in transformed NahG plants and etr-1 and
jar-1 mutants, to determined if these strains follows the SA-dependent or
independent way.
Biometrical parameter used to determined the PGPR effect were: perimeter
and area of the plants. Strains that produce best results in perimeter
compared with the control are N11.37, N17.35 and N19.27. When plant
area was analysed best results were obtained only with the strain N11.37.
It is interesting to indicate that although these bacteria produce significant
differences in PGPR effect on tomato, it does not happen in Arabidopsis. A
possible explanation might be that these bacteria were isolated from the rhizosphere
of Nicotiana glauca which are evolutionary much nearer to tomato
than to Arabidopsis. However, N11.37 gave good results also in tomato and
in Arabidopsis.
For ISR bioassays Xanthomonas campestris CECT 95 was selected as foliar
pathogen, according with experiments carried out in our lab, on tomato. The
six before cited strains were tested. Only N11.37 and N6.8 gave significant
differences compared with the control with only 20,6 and 21,7 % respectivesly
of disease incidence.
Finally, bioassays were carried out using NahG transplants, and ert-1 and
jar-1 mutants with N11.37 and N6.8. These experiment indicate that the
possible ISR-route followed by these bacteria are dependent of SA.
Bibliography
Pieterse, C. M. J et al. 2000. Pathology, 57: 123-134.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin