Plant Molecular Biology 52: 1011–1024, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
Regulation of CDPK isoforms during tuber development
, Delphine Chinchilla
and Rita Mar
Instituto de Investigaciones en Ingenier´ıa Gen´etica y Biolog´ıa Molecular, CONICET and Facultad de Ciencias
Exactas y Naturales, Universidad de Buenos Aires, Vuelta de Obligado 2490 2
piso, 1428 Buenos Aires, Argen-
author for correspondence; e-mail email@example.com);
Institut des Sciences V´eg´etales, Centre National
de la Recherche Scientiﬁque, 1 Avenue de la Terrasse, F-91198, Gif sur Yvette, France
Received 11 February 2003; accepted in revised form 26 May 2003
Key words: calcium-dependent protein kinases, differential expression, myristoylation, palmitoylation, Solanum
CDPK activities present during tuber development were analysed. A high CDPK activity was detected in the soluble
fraction of early stolons and a lower one was detected in soluble and particulate fractions of induced stolons.
The early and late CDPK activities displayed diverse speciﬁcity for in vitro substrates and different subcellular
distribution. Western blot analysis revealed two CDPKs of 55 and 60 kDa that follow a precise spatial and temporal
proﬁle of expression. The 55 kDa protein was only detected in early-elongating stolons and the 60 kDa one was
induced upon stolon swelling, correlating with early and late CDPK activities. A new member of the potato CDPK
family, StCDPK3, was identiﬁed from a stolon cDNA library. Gene speciﬁc RT-PCR demonstrated that this gene
is only expressed in early stolons, while the previously identiﬁed StCDPK1 is expressed upon stolon swelling.
This expression proﬁle suggests that StCDPK3 could correspond to the 55 kDa isoform while StCDPK1 could
encode the 60 kDa isoform present in swelling stolons. StCDPK1 has myristoylation and palmitoylation consensus
possibly involved in its dual intracellular localization. Transient expression studies with wild-type and mutated
forms of StCDPK1 fused to GFP were used to show that subcellular localization of this isoform is controlled
by myristoylation and palmitoylation. Altogether, our data suggest that sequential activation of StCDPK3 and
StCDPK1 and the subcellular localisation of StCDPK1 might be critical regulatory steps of calcium signalling
during potato tuber development.
Potato tuberization is an ideal model system to study
the regulation of gene expression during organ devel-
opment. Potato plants produce tubers as a result of
the changing balance of endogenous growth regulat-
ors, which is brought about by the plant’s ability to
perceive changing environmental conditions (Cutter,
The nucleotide sequence data reported will appear in the EMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accession numbers AF115406 (StCDPK1), AF418563 (StCDPK2)
and AF518003 (StCDPK3).
During the early stages of tuber formation the sto-
lons alter their growth habit, displaying a cessation
of elongation and the initiation of subapical radial
growth. Increased cell division and expansion are
followed rapidly by a massive deposition of starch
and storage proteins as a result of the coordinated
expression of genes involved in starch and protein bio-
synthesis (Prat et al., 1990; Visser et al., 1994). The
transformation of stolons into tubers impacts greatly
on the whole plant physiology because developing
tubers subsequently become the largest sinks present.
There have been many reports of the effects of
growth regulators on tuberization in potato, however
no unequivocal ‘tuberising’ factor has been identi-