Download Cell – cell communication in early seed development of Arabidopsis

Cell – cell communication in early seed development of
Arabidopsis thaliana
Katarzyna Gacek , Jose Gutierrez Marcos
[email protected]
University of Warwick, Warwick HRI, Wellesbourne, Warwick, CV35 9EF
1.Background:
4. Genetic interaction between iku2 and erecta
Reproduction and seed formation are the key events in the life cycle of
flowering plants. Normal development of the seed is achieved through
coordinated growth of its three components: embryo, endosperm and
maternal integuments. Recent genetic studies have revealed that the
coordinated growth of these components is mediated by intercellular cell
- cell communication 2. This mechanism is thought to involve leucine rich
repeat receptor like kinases (LRR LRK), small secreted peptides acting
as ligands and yet unknown enzymes processing both ligands and
receptors for their correct localisation. However, the regulation of these
processes remain largely unknown. In Arabidopsis, IKU2 encodes a LRR
RLK and is a key regulator of endosperm development and seed size3. It
has been shown that a reduced mutant endosperm growth correlates
with a decrease in cell elongation in maternal integuments 4, indicating
that a form of communication exist between the two seed components.
col
WT Col
er105 (Col)
iku2-4
iku2 (Col)
iku2-4/er105
iku2er105 (Col)
• To assess the possible genetic interaction between erecta and iku2, a
quantitative approach to proportional seed size measurements was
applied to single and double mutant line.
• er105/iku2 double mutant showed an enhanced seed phenotype when
compared to single er105 and iku2-4.
Seed development
in
g
te
ts
en
um
Percentage of large and small seeds measured as seed area (in pixels) in seed
progenies from WT and mutants in Columbia background.
endosperm
embryo
Col, wild-type; er105, homozygous erecta; iku2-4, homozygous iku2; er105iku2, double homozygous iku2 and
er105 mutant; er105/+iku2. heterozygous erecta and homozygous iku2; er105iku2/+, homozygous er105 and
heterozygous iku2. Red bars, large seeds; blue bars, small seeds.
Genetic interaction between IKU2 and ERECTA indicates that they are
both involved in the regulation of seed size
Cross section of Arabidopsis seeds illustrating different stages of endosperm and embryo development: (a)
Zygote stage of an embryo and four nuclei endosperm, (b) Globular embryo, free nuclear endosperm, (c)
Partially cellularised endosperm forms three distinctive domains: MIC micropylar, CHZ chalazal, incomplete
cellularised heart stage of an embryo, d) Fully cellularised endosperm, walking stick embryo. Arrows:
indicates possible cell-cell communication between the three seed components
er/erl1/erl2
2. Aim
To understand how endosperm, embryo and maternal integuments
coordinate seed growth and development.
3. IKU2 is a leucine rich repeat receptor like kinases (LRR
RLK) that regulates seed development in Arabidopsis.
iku2
cell elongation in
vegetative tissue
er
seed size
Diagram showing the biochemical interaction between ERECTA (er), ERECTA LIKE 1 (erl1) and ERECTA
LIKE2 (erl2) to regulate cell elongation in vegetative tissue and the possible interaction between IKU2 (iku2) and
ERECTA (er) to regulate seed size.
5. Forward genetic screen to identify modifiers of iku2
A
Diagram of IKU2 illustrating different domains and mutatant alleles
T-DNA mutagenesis
iku2-4
TDNA
iku2-2
iku2-1
G-A stop
iku2-3
35bp deletion
G-A
iku2-3
ARG - LYS
B
SP
TM
LRR
small seed (iku2-3)
KINASE
screen plants with
bigger seeds
SP: signal peptide, LRR: leucine rich repeat domain, TM: transmembrane domain, KINASE kinase
domain
iku2-3 modifier
A
B
C
D
E
Diagram representing the strategy to identify modifiers of IKU2 by T-DNA mutagenesis.
A, small seeds from an iku2-3 plants; B, small and large seeds (arrows) from a mutagenised iku2-3 plant.
Columbia WT
iku2-4 (Col)
Landsberg erecta WT
iku2-1 (Ler)
iku2-3 (Ler)
• This strategy can be used to identify all the genetic modifiers of iku2-3
The phenotype of Arabidopsis thaliana wild type and iku2 mutant seed. A. Wild-type Columbia ecotype; B. iku2-4
in Columbia; C. Wild-type Landsberg erecta; D. iku2-1 in Lansberg erecta; E. iku2-3 in Landsberg erecta.
• Phenotype of the iku2 mutation is more severe in
Landsberg erecta than in Columbia genetic background.
• Landsberg erecta ecotype carries a natural mutation in the
erecta gene that also encodes a LRR RLK
• Hypothesis: the erecta mutation enhances iku2 seed
phentoype
6. Conclusions and future work
• IKU2 regulates seed size by interacting with other RLK such as
ERECTA.
• Future work will focus on the identification of novel modifiers and
potential ligands of IKU2.
References:
1. GARCIA, D., FITZ GERALD, J. N. & BERGER, F. (2005) Maternal control of integument cell elongation and zygotic control of endosperm growth are coordinated to determine seed size in Arabidopsis. Plant Cell, 17, 52-60.
2. BERGER, F., GRINI, P. E. & SCHNITTGER, A. (2006) Endosperm: an integrator of seed growth and development. Current Opinion in Plant Biology, 9, 664-670.
3. GARCIA, D., SAINGERY, V., CHAMBRIER, P., MAYER, U., JURGENS, G. & BERGER, F. (2003) Arabidopsis haiku mutants reveal new controls of seed size by endosperm. Plant Physiol, 131, 1661-70.
4. LUO, M., DENNIS, E. S., BERGER, F., PEACOCK, W. J. & CHAUDHURY, A. (2005) MINISEED3 (MINI3), a WRKY family gene, and HAIKU2 (IKU2), a leucine-rich repeat (LRR) KINASE gene,
Acknowledgments:
The University of Warwick for support.