Isolation and functional characterization of pectin methylesterase inhibitor (PMEI) genesin durum wheat (Triticum durum Desf)
Author(s)
Rocchi, Valentina
Date Issued
March 22, 2011
Type
Doctoral Thesis
Abstract
One of the main goal of breeding programs is the development of crop varieties that simultaneously
control different pathogens. This can be obtained by improving the pre-existing plant defence
mechanisms such as the structure and composition of the plant cell wall, which is one of the first
barriers encountered by the microbial pathogens during plant tissue colonization. To overcome this
obstacle, most fungal pathogens produce a variety of enzymes that degrade the wall polysaccharides;
among them, pectin degrading enzymes are among the first to be secreted by the pathogens to enter
and spread into the plant tissue.
Pectin in the plant cell wall is secreted in a highly methylesterified form and is demethylesterified in
muro by pectin methylesterase (PME). PME activity contributes to modify the structure of pectin,
affecting also the susceptibility to hydrolytic attack of pathogen pectin degrading enzymes. The
activity of PME is regulated by specific interaction with a protein inhibitors (PMEIs). Since the
modification of pectin are associated with important plant physiological processes and also with plant
defence response, the interaction PME-PMEI can have an important biological role.
In wheat, genes encoding for pectin methyelesterase inhibitor have not been characterized, for this
reason during this work three different genes Tdpmei2.1, Tdpmei2.2, Tdpmei7.3 were characterized
from durum wheat cv. Svevo. It has been demonstrated that these genes encode for functional inhibitor
able to reduce the PME activity of Orange peel PME (OpPME). Moreover, the TdPMEI2.1,
TdPMEI2.2 e TdPMEI7.3 are able to inhibit the endogenous wheat PME activity, showing a
specificity against PME activity from different wheat tissues. All the three inhibitors do not show
inhibitory capability against microbial PME.
Tdpmei2.1 e Tdpmei2.2 have been localized on the long arm of chromosome group 2 and their
sequence is strongly conserved in wild wheat progenitors.
To shed light on the possible physiological role of these inhibitors, the transcript accumulation of
Tdpmei2.1, Tdpmei2.2 and Tdpmei7.3 has been investigated. Results show that trascripTdpmei2.2 and
Tdpmei7.3 undergo intron retention. The complete removal of intron of both genes is observed only in
anther tissue. Differently, the Tdpmei7.3 transcript accumulated in all tissue analyzed but strongly in
stem tissue.
Transcript accumulation of Tdpmei genes has been investigated also following infection with the
fungal pathogen Bipolaris sorokiniana, but no increase in the level of transcripts was observed.
To verify the capability to modulate in planta the wheat endogenous PME activity, wheat
transgenic wheat plants overexpressing the Tdpmei7.3 were produced. T0 plants showed
different level of PME activity reduction that varied from about 10% to 85% of the control PME
activity.
Additional information
Dottorato di ricerca in Biotecnologie vegetali
Subjects
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