Proceedings of the XLVI Italian
Society of Agricultural Genetics - SIGA Annual Congress
Giardini
Naxos, Italy - 18/21 September, 2002
ISBN 88-900622-3-1
Poster
Abstract - 5.20
Oligogalacturonides
Inhibit the induction of Late but not of Early Auxin-Responsive Genes Involved
in Differentiation
MAURO M.L.*, DE LORENZO G.**, BELLINCAMPI
D.**
*) Dipartimento di Genetica e
Biologia Molecolare
**) Dipartimento di Biologia Vegetale
Università "La
Sapienza"di Roma, P.le Aldo Moro 5, 00185 ROMA
auxin-regulated genes,
oligogalacturonides, differentiation, tobacco
From recent studies in animals and plants
the notion has emerged that disease resistance mechanisms and developmental
processes may share regulatory signals .Oligogacturonides (OG), well known
elicitors of plant defence responses, exhibit various regulatory effects on plant growth and differentiation.
OGs are generally
considered localised active signals and the effects induced by OGs in plant
defence and development are considered to be receptor-mediated.
The analysis of
different responses produced by OGs suggests the existence of different
pathways leading to the activation of defence responses or the regulation of
developmental processes. In many of these
latter effects OGs seem to act as
antagonists to auxin.
To investigate on the mechanism of the
antagonism of OGs to auxin, we analysed the effect of different
auxin-responsive promoters of genes likely to be involved in developmental and growth processes.
Auxin-responsive
genes are classified as early or late-responsive on the basis of the kinetics
of their response to the
hormone. In this work, we examined genes belonging to both classes.
Analysis
by GUS reporter gene shows that submicromolar concentrations of OGs with a DP
of 9 to 18 inhibit the late auxin-regulated activation of the promoters of the
genes pNt114 from tobacco, prolB and prolD from Agrobacterium rhizogenes in tobacco seedlings. In contrast, OG concentrations as high as
100 mg/ml, do not affect the early activation
of pGm-GH3 from soybean, indicating
that this promoter responds
to auxin via an OG-insensitive signal
transduction pathway.
To confirm our results, we analysed by
RNA gel blot the effect of OGs on two additional early auxin-responsive tobacco
genes: Nt-gh3, a GH3 related gene and Nt-iaa 2.3/Nt-iaa 2.5, belonging to the Aux/IAA large multigene family. We demonstrate that, in addition to pGm-GH3 these
early responsive genes are insensitive to OGs. Moreover
histochemically analysis shows that the inhibitory effect exerted by OGs was
not tissue-specific. The OG effect is not correlated with the auxin concentration necessary to
activate the genes. These results taken toghether with a comparative analysis
of promoter sequences suggest the possibility that OG-triggered transduction
pathway(s) intersect(s) those induced by auxin far downstream of the perception
event. A model of OG as auxin antagonist will be presented. The signalling element(s) at the intersection(s)
between the OG and IAA transduction networks remains to be identified.