Plant Molecular Biology 33: 87–95, 1997.
1997 Kluwer Academic Publishers. Printed in Belgium.
-glucanase expressed at high levels in rapidly expanding
David A. Brummell
, Colin R. Bird
, Wolfgang Schuch
Mann Laboratory, Department of Vegetable Crops, University of California, Davis, CA 95616, USA (
Zeneca Plant Science, Jealott’s Hill Research Station, Bracknell, RG42 6ET, UK
Received 1 May 1996; accepted in revised form 24 September 1996
Key words: auxin, cell expansion, cellulase, endo-1,4-
-glucanase,ethylene, gene expression
and fruit ripening, are accompanied by increased enzyme activity and mRNA abundanceof endo-1,4-
(EGases). An EGase cDNA clone, Cel4, isolated from tomato (Lycopersicon esculentum) has been shown to be
identical to a tomato pistil-predominant EGase cDNA, TPP18. In addition to its previously reported expression
during certain stages of early pistil development, Cel4 mRNA was also detected at high levels in the growing zones
of etiolated hypocotyls (about 2.5-fold less than in pistils) and in young expanding leaves (about 3.5-fold less than
in pistils). The abundanceofCel4mRNAdeclinedprecipitouslyinoldertissuesascells becamefully expanded,and
was barely detectable in mature vegetative tissues. Cel4 mRNA abundance was also low in abscission zones, and
did not increase as abscission progressed. In fruit, Cel4 mRNA was present at low levels during fruit expansion, but
was essentially absent during subsequent fruit development and ripening. Treatment of etiolated hypocotyls with
ethylene or high concentrations of auxin sufﬁcient to induce rapid lateral cell expansion and hypocotyl swelling
also brought about an approximate doubling of Cel4 mRNA abundance, suggesting that Cel4 mRNA accumulation
may be promoted directly or indirectly by ethylene. Thus, accumulation of Cel4 mRNA was found to be correlated
with rapid cell expansion in pistils, hypocotyls and leaves.
-D-glucanases (EGases, EC 22.214.171.124) are
enzymes that hydrolyze polysaccharides possessing a
-glucanbackbone,and have been proposed to act
primarily on xyloglucan in the plant cell wall .
Increased extractable EGase enzyme activity is asso-
ciated with many developmental events that involve
architectural modiﬁcation of the cell wall , includ-
ing fruit ripening [15, 26], differentiation of vascular
tissue , developmentof ﬂower reproductiveorgans
[8, 23], leaf and ﬂower abscission [28, 31], and cell
expansion . In many tissues, EGase enzyme activ-
ity levels appear to be under hormonal control. For
example, ethylene treatment of bean abscission zones
promotes the abscission process concomitant with an
EGase protein, and its corresponding mRNA, indicat-
ing that this class of EGase is ethylene regulated at the
level of mRNA abundance [28, 34]. Auxin regulated
EGases have also been described, with auxin treatment
lar cells [21, 22, 25] increasing EGase enzyme activity
and mRNA levels.
and hormonal regulation of their expression, EGases
have been shown to be encoded by multi-gene fam-
ilies in several higher plant species [3, 10, 18, 23].
A major goal in recent years has been to characterize
the complexity of the EGase gene family and to assign
functional roles to individual gene family members
[10, 16, 18, 23]. Individual members of EGase multi-
gene familiesdescribedto date possess unique patterns
of tissue-speciﬁc and temporal expression [10, 18, 20,
23], implying that each plays a particular deﬁned role
in plant development.