Research Overview
Research Group:
Identification and Characterization of the Plant Genes
Controlling Important Agronomic Traits
I. Introduction
Research focus
1. Identification and functional characterization of genes controlling cotton fiber
development
2. Isolation and functional analyses of genes encoding for salt resistance in
halophytes
Group Members
- Principle investigator: Gui-Xian Xia, Professor, Ph. D. (1993, Geneva University,
Switzerland)
- Other members:
Senior research assistant: Gui-Ling Wang
Senior research assistant: Nai-Qin Zhong
Research assistant: Hai-Yun Wang
And 8 graduate students
II. Research Background and Significance
1. Cotton fiber development
Cotton fiber is a single epidermal cell of the outer integument of the ovule. The
development of cotton fiber can be divided into four stages: initiation, elongation,
secondary wall synthesis and maturation. Developing fibers exhibit two striking
features: 1) rapid and spontaneous growth in the absence of cell division during
elongation stage; 2) exclusive synthesis of cellulose during secondary wall formation
phase. Based on these characters, cotton fiber is considered as an ideal model for
studying plant cell elongation and cell wall biogenesis. To date, the molecular
mechanisms controlling fiber elongation and wall synthesis remain largely unknown.
The main research focus in our group is to identify genes that are expressed
specifically in developing fibers and to elucidate their roles in cell elongation and
secondary wall formation. Our ultimate goals are to improve our understanding about
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the regulation of cell elongation and cell wall synthesis in higher plants through fiber
system，and to provide useful genes for the modification of fiber quality via genetic
engineering.
2. Halophyte salt tolerance
Soil salinity is one of the important limiting factors for plant growth and
development. Studies on the salt resistance in halophytes can advance our knowledge
about the mechanisms by which higher plants gain salinity tolerance. Thellungiella
halophia is an excellent model halophytic system for the research of plant salt
tolerance owing to its Arabidopsis-like characteristics such as a small genome, short
life cycle, high seed yield and easy transformation. Besides T. halophia, the Suaeda
salsa is also an attracting extremophile for studying salt resistance mechanisms in
halophytes.
Another research interest in our group is to identify salt resistance-related genes
from T halophia and S salsa and to characterize their roles in the process of plant
adaptation to salinity. Our goal is to exploit candidate genes for genetic manipulation
of salinity resistance in agriculturally important crops.
III. Major Achievements
1. Cotton fiber development
We have identified several fiber-specific genes using SSH and FDD techniques.
Of which, three genes encoding an actin depolymerizing factor (GhADF1), a profilin
isoform (GhPFN1) and a receptor-like kinase (GhRLK1), respectively, were studies
more extensively. Transgenic cotton plants with inhibited expression of GhADF1
exhibited increased fiber strength; ectopic overxpression of GhPFN1 in tobacco
suspension cells resulted in enhanced cell elongation accompanied with a structural
change in the actin cytoskeleton; accumulation of GhRLK1 transcripts is tightly
associated with secondary wall synthesis in fiber cells and the gene product is a
functional kinase with serine/threonine and tyrosine dual specificities. We also
assessed the function of a fiber-specific expansin gene (GhPFN1) by a transgenic
approach. GhEXP1-overexpreesing cotton fibers showed enhanced fiber strength with
higher amounts of total and crystallized cellulose.
Four important points can be drawn from our data: 1) actin cytoskeleton
modulators such as GhADF1 and GhPFN1 have important roles in rapid elongation
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and secondary wall synthesis in fiber cells; 2) the receptor-like kinase GhRLK1 may
participate in the signal transduction controlling active cellulose synthesis during fiber
development; 3) the GhEXP1 functions in controlling cellulose synthesis and crystal
cellulose content during the process of secondary wall formation; 4) GhADF1 and
GhEXP1 are good candidate genes for the genetic modification of fiber quality.
2. Halophyte salt resistance
Using fission yeast as a simple functional system, we have identified a number of
salt tolerance-related genes from T halophia and S salsa by screening salt-resistant
transgenic yeast clones. Four candidate genes were selected for more detailed
analyses, including two genes from T halophia (ThCpR1 encoding a cycloporin and
ThQP1 encoding an aquoporin) and one gene from S salsa (SaTYPA1 encoding a
GTP-binding protein). Expression of these genes is salt stress-inducible and ectopic
overepression of them in Arabidopsis or tobacco led to increased salt tolerance. We
also isolated a gene encoding an DREB transcription factor (PpDREB1) from the
extremophile moss P patens. Overexpression of PpDREB1 in tobacco BY-2 cells
resulted in markedly increased salt and drought resistance.
Our results provided experimental evidence for the participation of the
aforementioned genes in achieving salt resistance in the corresponding extremophile.
As these genes are able to confer salinity tolerance to the glycophyte transgenics, they
can be considered for utilization in generation of GM crops.
Publications
1. Zhan-Liang Qu, Hai-Yun Wang and Gui-Xian Xia (2005) GhHb1: a nonsymbiotic
hemoglobin gene of cotton responsive to infection by Verticillium dahliae.
Biochimica et Biophysica Acta - Gene Structure and Expression (in press)
2. Hai-Yun Wang, Yi Yu, Zhi-Ling Chen and Gui-Xian Xia (2005)
Functional characterization of Gossypium hirsutum Profilin 1 gene (GhPFN1) in
tobacco suspension cells. Planta (in press)
3. Yuan-Li Li, Jie Sun and Gui-Xian Xia (2005)
Cloning and characterization of an LRR receptor-like protein kinase gene
associated with cotton fiber development. Molecular Genetics and Genomics 273
(3 ): 217 – 224.
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4. Jia Shirong (Editor in Chief), Guo Sandui, An Daochang, Xia Guixian (2004)
Transgenic Cotton, Science Press, Beijing/New York
5. Peng Gao, Gui-Xian Xia, Tian-Zhen Zhang (2004)
Progress in Cotton Genomics. In: Cheng-Sen Li(Ed), Progress in Plant Sciences,
Higher Education Press, Beijing, Vol.6, pp237-248.
6. Jie Sun, Yuan-Li Li, Ruo-Hai Wang, and Gui-Xian Xia (2004）
Identification of genes that specifically/preferentially expressed in developing
cotton fibers by mRNA fluorescence differential display (FDD)
Chinese Journal of Biotechnology 20 (1): 39－42.
7. Zhi-Ling Chen, Hao-Hiao Ouyang, Xiang-Lin Liu and Gui-Xian Xia (2003)
The role of cortical microtubules in moss protonemal cells during dehydration/
rehydration cycle.
Chinese Journal of Biotechnology 19 (3): 317-321.
8. Yuan-Li Li, Jie Sun, Chun-Hong Li, Yong-Qing Zhu and Gui-Xian Xia (2003)
Preferential expression of a -tubulin gene (GhTub1) in developing cotton fibers.
Science in China (Series C), 46 (3): 235-242.
9. Ya-Xiong Tang, An-Ping Chen, Shi-Gui Liu and Gui-Xian Xia (2003)
Identification and functional characterization of a salt tolerance-related gene
(AtGRP9 ) of Arabidopsis. Progress in Natural Science 1(13): 50-54.
10.Li-Hong Li, Hai-Yun Wang, Yan Li and Gui-Xian Xia (2002)
Expression of a cotton profilin gene GhPFN1 is associated with fiber cell elongation.
Progress in Natural science 12 (10):794－797.
11.Dong Wang, Li-Hong Li, Zhi-Ling Chen and Gui-Xian Xia (2002)
Characterization and pilot functional study of a root-specific MYB transcription
factor of Arabidopsis. Chinese Science Bulletin 47(4): 297-301.
12.Chun-Hai Dong, Gui-Xian Xia (co-first author) Yan Hong, Srinivasan
Ramachandran, Benedikt Kost, and Nam-Hai Chua (2001) ADF proteins are
involved in the control of flowering and regulate F-actin organization, cell
expansion and organ growth in Arabidopsis. The Plant Cell 13: 1333-1346.
Patent
1． Gui-Xian Xia, Yuan-Li Li, Jie Sun.
The cDNA sequence and application of the cotton fiber-specific gene GhRLK1.
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Patent Application Number: 03141157.6.
2. Gui-Xian Xia, Hia-Yun Wang, Yan Li, Guiling Wang, Gaili Jiao.
The full length cDNA of cotton fiber-preferential gene GhADF1 and its transgenic
cotton. Paten Application Number: 200510085071.7.
IV. Future Research Plan
1. Interaction between cytoskeleton and cell wall in fiber cells
The functional relationship between cytoskeleton and cell wall is an intriguing
research subject. As ADF is a key modulator of dynamic organization of actin
cytoskeleton and that expansin plays a key role in cell wall expansion, and because
that both GhADF1 and GhEXP1 transgenic plants showed altered cell wall
organizations, we attempt to see if the cytoskeleton structures are varied in the
GhADF1 transgenic fibers, and if so, how changed cytoskeleton organizations lead to
alterations in the secondary wall structure; we are also interested in knowing how
increased GhEXP1 levels promoted synthesis and crystallization of the cellulose and
what happened to the cytoskeleton structures in the GhEXP1-overexprerssing fibers.
Understanding the functional links between cytoskeleton and cell wall in fiber cells
will certainly provide more insight into the mechanisms controlling cell wall synthesis
and organization in higher plant cells.
2. Signal transduction involving GhRLK1
To date, very little is known about the signal transduction pathways regulating
fiber development. Since it is highly possible that GhRLK1 is a component in the
signal transduction pathway controlling onset and active secondary wall synthesis,
efforts will be made to identify the upstream ligand and downstream targets of
GhRLK1 in order to decipher the pathway eventually. Meanwhile, the cellular
function of GhRLK1 will be further analyzed by evaluating the phenotypes of the
GhRLK1 transgenic fibers.
3. Participation of ThCyP1, SaTYP A1 and PpDREB1 in salt stress signaling
As ThCyP1 and SaTYPA1 and PpDREB1 are putative signaling components, we
will endeavor to identify their upstream and downstream molecules. In the mean time,
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functional analyses by cellular, biochemical and transgenic approaches will be
continued depending on the nature of the individual genes. Also, the roles played by
these genes in halophytes will be compared with those exhibited by their counterparts
in glycophytes.
4. Application
Although overexpression of genes with an extremophile-origin such as ThQP1,
ThCyP1, SaTYPA1 and PpDREB1 are able to confer enhanced salt tolerance to the
transgenic glycophytes，it is not known if such salt tolerance can be stably maintained
in the subsequent generations. To further exploit the application potential of these
genes in the genetic engineering aimed to improve crop salt tolerance, maintenance of
the salt resistance in the offspring of the transgenic plants will be examined.
Likewise, GhADF1 and GhEXP1 transgenic cotton plants will be tested for stable
inheritance of the improved fiber quality traits.
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