CEPCEB Members
Patricia S. Springer
Associate Professor of Genetics
Department of Botany and Plant Sciences
2203
Batchelor Hall
University of California
Riverside, CA 92521
Phone:
(951) 827-5785
Fax: (951) 827-4437
| Areas
of Expertise | - Genetics
- Molecular
Biology
- Plant Development
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| Background I
received a B.S. in Genetics and Cell Biology from the University of Minnesota
in 1985 and a Ph.D. in Biology from Purdue University in 1992. My dissertation
research, which was carried out under the guidance of Jeff Bennetzen, investigated
the organization of repetitive DNA sequences in the maize genome and the role
of DNA methylation in regulating transposable element activity. I was a
Postdoctoral Fellow at Cold Spring Harbor Laboratory, in Rob Martienssen's lab.
As a postdoc, I worked on the development of a gene trap system in Arabidopsis.
This approach uses a reporter gene, which has been randomly integrated into the
genome, to identify genes based on expression. When reporter gene insertion occurs
within or nearby a chromosomal gene, the reporter gene "reports" expression
of the chromosomal gene, allowing gene identification on the basis of an expression
pattern. I came to UCR as an Assistant Professor in 1997. My research interests
lie in understanding organogenesis in plants. The shoot apical meristem (SAM)
is a population of cells that serves as the source of all of the above ground
tissues of a plant. Very little is known about the molecular mechanisms controlling
the function of this critically important structure. Research in my laboratory
focuses on the molecular genetics of shoot apical meristem function, with emphasis
on the role that the SAM plays during the early events of leaf development. We
have exploited the gene trap system to isolate genes that are specifically expressed
in the SAM and/or surrounding cells, in order to identify components that are
involved in SAM function. We identified three genes whose expression marks sub-domains
of the SAM, and several other genes that are expressed in domains that do not
appear to correspond to known anatomical features. Our current efforts focus on
understanding the role that these genes play in SAM functions. We are using a
combination of genetics, functional genomics, molecular, and cellular techniques
to address these issues.
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The LATERAL ORGAN BOUNDARIES Gene
The LATERAL ORGAN BOUNDARIES (LOB) gene is expressed at the leaf base in a
domain that defines a boundary between the meristem and the leaf. This expression
pattern suggests a role in boundary establishment and organ separation, events
that are critical for proper leaf development. In addition, LOB expression is
regulated by the homeobox transcription factors SHOOT MERISTEMLESS (STM) and KNAT1,
and the MYB-domain protein ASYMMETRIC LEAVES1 (AS1). STM and AS1 negatively regulate
each other and no targets of either transcription factor have been identified.
LOB expression requires the activities of both AS1 and STM may therefore yield
important information about their functions. LOB encodes a novel, plant-specific
protein that is not similar to any proteins of known function. The LOB protein
contains a conserved amino acid domain (the
LOB domain) that is found in
42 other Arabidopsis proteins. Loss-of-function mutations in LOB do not cause
conspicuous morphological changes, suggesting that LOB is functionally redundant.
Expression of LOB outside of its normal domain has several morphological effects
that are in part due to changes in cell division. We are using functional genomic
approaches to investigate the role of the LOB-Domain (LBD) containing proteins
in plant development. We have used phylogenetic analyses to identify LBD genes
that are most closely related to LOB. Our current efforts are focused on identifying
mutations in these genes.
 |
| GUS activity in the ET22 (LOB::DsE)
enhancer trap line. A. 4-day-old seedling; arrow marks cells at base of cotyledons,
arrowhead marks cells at base of leaf primordia. (B) Transverse section through
9-day-old seedling apex showing GUS staining on the adaxial side of leaf bases.
S = SAM; lp = leaf primordium. (C) Inflorescence showing GUS activity at the base
of flower pedicels and floral organs. | Important
information about the role of the LBD genes came from the discovery that
the classic mutant asymmetric leaves2 corresponds to the LBD6 gene.
AS2 is required, together with AS1, for the repression of KNOX
genes in differentiated lateral organs. KNOX genes are normally expressed
in the SAM and are down-regulated in initiating lateral organ primordia, an event
that is critical for the proper development of differentiated tissues. AS1
and AS2 play an important role in maintaining KNOX-gene repression
in the leaf. In addition, we have shown that overexpression of AS2 results
in alterations in lateral organ polarity, implicating AS2 in the regulation
of adaxial cell fates. Our current efforts are focused on trying to understand
the role that AS2 plays in polarity establishment.
 |
| 35S:AS2
plants form abnormal lateral organs. A. Wild type. B-D. 35S:AS2. Arrow
in C points to abaxial protrusion. E-F. Cross sections (adaxial side up) through
wild type leaf (E) and 35S:AS2 leaf (F). p=palisade, s=spongy mesophyll,
pl=palisade-like. |
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to Top
The VASCULAR PREPATTERN Gene
| VASCULAR
PREPATTERN (VPP) is expressed in cells that are destined to differentiate
into vascular tissue. VPP expression predicts vascular tissue differentiation,
suggesting that VPP may play a role in setting up vascular pattern. VPP
expression occurs earlier than any known vascular gene, and as such is an extremely
powerful marker for studying vascular development. VPP encodes a novel,
plant-specific protein of unknown function and defines a new gene family of 17
genes in Arabidopsis. Mutations in VPP show no obvious phenotype suggesting
that VPP is functionally redundant. Experiments are underway to express
VPP outside of its normal domain in order to determine if vascular pattern
can be altered. We are currently characterizing the VPP gene family in
order to identify genes that may share overlapping function with VPP. | | GUS
activity in the ETR273 enhancer trap line reports VPP expression and predicts
vascular cell identity. | |
MYB-domain
genes in leaf development
MYB105 and MYB117 are two
related MYB-domain genes that are expressed at the base of leaves and other lateral
organs, in a pattern similar to that of LOB. MYB105 and MYB117 encode
R2R3-type MYB proteins and belong to a small subgroup of MYB proteins that share
a conserved motif at their carboxy-termini. Among the 7 proteins in this clade,
MYB105 and MYB117 are most closely related to each other. Loss-of-function mutations
in MYB105 and MYB117 do not result in conspicuous phenotypes. Based
on their sequence similarity and similar expression patterns, it is likely that
MYB105 and MYB117 have overlapping functions. Double-mutant analyses
are ongoing and should help to clarify this issue. Ectopic expression of either
MYB105 or MYB117 results in phenotypes that may be informative with regard
to their function. Ectopic expression of either gene causes the formation of leaves
that resemble the as2 mutant, suggesting a possible interaction between
these MYB genes and AS2. In addition, ectopic expression of MYB105
results in the formation of flowers that produce ovules on the outside of the
carpel, a phenotype indicative of polarity defects. Thus, MYB105 and MYB117
may also play a role in the development of adaxial-abaxial polarity in leaves
and other lateral organs. We are currently working toward an understanding of
the function of MYB105 and MYB117 in lateral organ development. |  GUS
activity reports MYB117 expression. A-C. Expression on the adaxial side of the
rosette leaf base. A. Side view, B. Top view, C. Cross section. D. Expression
in the inflorescence shoot. Longitudinal section viewed in dark field, GUS activity
appears pink. | Current
Laboratory Personnel |
- Aman Husbands, graduate student
-
Barbara Jablonska, technician
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Venkateswari Jaganatha, postdoc
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Dong-keun Lee, graduate student
-
Wan-Ching Cathy Lin, postdoc
-
Amanda Mangeon, graduate student
-
Sonia Zarate, graduate student (joint with Linda Walling Lab)
Selected
Publications (Bibliography
page)
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