Plant Molecular Biology 37: 121–129, 1998.
1998 Kluwer Academic Publishers. Printed in Belgium.
Isolation and characterization of a functional A-type cyclin from maize
Wen-Ling Hsieh and Stephen M. Wolniak
University of Maryland, Department of Plant Biology, College Park, MD 20742, USA (
Received 7 March 1997; accepted in revised form 12 December 1997
Key words: cell cycle, complementation, cyclins, maize, root meristem
Cyclins areinvolvedin theregulation ofcell cycleprogressionin eukaryotes.We haveisolated a cyclin cDNA clone,
cycZm2w,frommaizeroottip cells, whichﬁtsbestintogroupA2ofcurrentplantcyclingeneclassiﬁcationschemes.
The cDNA encodes a protein with a domain homologous to the cyclin box of mitotic cyclins. Complementation
studies revealed that cycZm2w was able to rescue a budding yeast cyclin-deﬁcient mutant (BF305–15d#21). As
expected, cycZm2w is expressed in organs of the maize plant that possess meristematic activity, but is especially
prominent in the proliferating regions of the root apex.
progression in eukaryotic cells. They were originally
discovered in sea urchin embryos as proteins that were
gressed rapidly through early embryogenic cell cycles
yeast demonstrated that cyclins are important in reg-
ulating progression through major checkpoints during
the cell cycle through their interaction with a cell divi-
sion cycle-dependent protein kinase [19, 35, 36], now
knownas cdk (for cyclin-dependentkinase).Biochem-
ical analyses of extracts from embryos of Xenopus
laevis [16, 17, 31] demonstrated that both cdk and
cyclin were integral parts of MPF (mitosis promoting
factor). Cyclins not only determine the activity of cdk,
but also regulate substrate speciﬁcity, subcellular loc-
alization, and stability of the kinase. At least eight
distinct cyclins have been identiﬁed under different
classiﬁcation systems in vertebrates ([35 for review]),
including the mitotic cyclins (cyclins A and B1-B3,
cyclins (cyclins C, D1-D3, E, G) and at least
two groups of cyclin-like proteins (cyclins F and H).
Thenucleotidesequencedata reportedwill appear in theEMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accession number U50064 (cycZm2w).
Consensus nucleotide sequences and conserved amino
acid motifs underlie cyclin classiﬁcation groupings.
The plant cyclins identiﬁed thus far fall into three
clusters [25, 40, 47]. Many of the known plant cyc-
lins show sequence homologies that are intermediate
between the discrete A- and B-types of animals and
fungi[12, 13, 20, 25, 39]. Apparentcyclinhomologues
have been isolated and characterized from a variety of
plant species, including carrot , soybean [20, 25]
Arabidopsis [7, 12, 13, 15, 21, 47], alfalfa [22, 32,
45], Antirrhinum , Brassica , tobacco [25, 37,
38], rice , and maize . A common technique
used to demonstrate the function of putative cyclin
cDNA clones is through functional complementation;
heterologous, expressed cyclin cDNAs are used either
restore cell cycle progression under restrictive condi-
tions in transformed conditional yeast cyclin mutants.
A-type cyclins from Arabidopsis, maize and soybean,
appear to function at the G
/M transition and can
induce maturation in oocytes of Xenopus [20, 21, 39].
Certain cyclinsfromsynchronizedalfalfa culture cells,
from ﬂoral meristems of Antirrhinum and from shoot
apices of soybean appear to function only in late G
and M [14, 22, 25, 32, 45]. The G
cyclins found in
plants form a family of cyclin D homologues  that
exhibit a conserved retinoblastoma protein interaction