Plant Molecular Biology 53: 581–595, 2003.
© 2003 Kluwer Academic Publishers. Printed in the Netherlands.
The elongation defective1 mutant of Arabidopsis is impaired in the gene
encoding a serine-rich secreted protein
Kvin Lertpiriyapong and Zinmay Renee Sung
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA (
correspondence; e-mail firstname.lastname@example.org)
Received 9 July 2003; accepted in revised form 24 October 2003
Key words: Arabidopsis, elongation defective 1 mutant, extracellular protein, ELD1-GFP, ELD1-related genes,
Coordinated cell growth and differentiation is crucial for the development of higher plants. Using the elongation
defective 1-1 (eld1-1) mutant, we cloned the ELD1 gene, which encodes a serine-rich protein. Genes homologous
to ELD1 can be found in plants, including Arabidopsis, rice, and tobacco, but not in other organisms. Using reverse
genetics, we identiﬁed a new allele, eld1-2, which is phenotypically indistinguishable from eld1-1, but does not
produce a detectable ELD1 transcript. The ELD1 gene sequence is the same as that of the KOBITO1 sequence.
However, the kob1 mutants display weak phenotype relative to the two eld1 mutants, which are likely null alleles.
KOB1 was reported to be a membrane protein involved in cellulose synthesis. However, based on ELD1-GFP
localization in plasmolyzed cells, we found that ELD1 is localized to the cell wall/extracellular matrix, rather than
the membrane. Thus, ELD1/KOB1 is a secreted protein involved in promoting cell growth. To investigate the rela-
tionship between ELD1 and Arabidopsis genes with high sequence similarity, we analyzed the possible subcellular
location of their proteins as well as their amino acid sequence. The ELD1-related proteins in Arabidopsis were
predicted to be localized to subcellular compartments different from that of ELD1. Thus, ELD1 is likely to be
functionally distinct from related Arabidopsis genes. These results suggest that ELD1 is a single-copy gene which
belongs to a small family of plant-speciﬁc genes with diverse function.
Plant cells typically expand 10- to 1000-fold in volume
before reaching maturity. Thus, plant body size is
largely reﬂected by cell size, not cell number. Plant
cells grow by enlarging the vacuole through water up-
take, with very minimal expansion of the cytoplasm.
The extent of cell growth is regulated by turgor pres-
sure, which is mainly attributed to the change in the
rigidity of the cell wall (Cosgrove, 1997). Cell growth,
therefore, requires genes controlling the modiﬁcation
and synthesis of cell wall materials and water uptake.
Many environmental and endogenous factors, such as
light, temperature, hormones, and positional signals
regulate the extent of cell growth in various tissues and
organs (Cosgrove 2000; Martin et al., 2001).
By means of growth-defective mutants, a large
number of genes regulating cell growth have been
identiﬁed. For instance, brassinosteroid-insensitive1
(bri1), diminuto/dwarf1 (dim/dwf1), deetiolated
(det)2, and constitutive photomorphogenesis and
dwarﬁsm (cpd) are mutants altered in genes in-
volved in either brassinosteroid synthesis or percep-
tion (Clouse et al., 1996; Szekeres et al., 1996;
Fujioka et al., 1997; Klahre et al., 1998). Procuste
(prc)andkorrigan (kor) are impaired in one of the cel-
lulose synthase subunits and endo-1,4-β-D-glucanase,
respectively (Nicol et al., 1998; Fagard et al., 2000).
These ﬁndings demonstrate the importance of cell wall
modiﬁcation and synthesis and growth hormone in the
regulation of cell growth. Moreover, the det3 mutant
is impaired in a vacuolar H
-ATPase subunit C, con-
ﬁrming the requirement of proper ionic regulation in