Department of Botany & Plant Sciences

Patricia S. Springer

Associate Professor of Genetics (Ph.D., 1992, Purdue University)
Office: 3107B Genomics Building
Phone: (951) 827-5785
Fax: (951) 827-5155
Email: patricia.springer@ucr.edu

Areas of Expertise

• Genetics
• Molecular Biology
• Plant Development

Background
The LATERAL ORGAN BOUNDARIES Gene
The VASCULAR PREPATTERN Gene
Current Laboratory Personnel
Selected Publications (Bibliography page)

​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.

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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.

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​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.

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​Current Laboratory Personnel

Aman Husbands, graduate student

Barbara Jablonska, technician

Venkateswari Jaganatha, postdoc

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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