CEPCEB Members

Elizabeth M. Lord Professor of Botany and Developmental Biology Vice Provost, Academic Personnel (Ph.D., University of California, Berkeley, 1978) 365 Surge Building University of California, Riverside 92521 Phone (951) 827-2304 FAX (951) 827-6226 Areas of Expertise Pollination Pollen Tube Guidance Pistil ECMs Adhesion
Background Selected Publications in Cell and Developmental Biology (Bibliography page) Current Laboratory Personnel and Projects

Background

My interests are in plant cell and developmental biology, with an emphasis on flower organ growth and pollination. One major focus in my lab now is the role of the gynoecium in pollination. Our model is that interaction between the transmitting tract extracellular matrices (ECMs) of the gynoecium or pistil, and the pollen tube, act to guide the tube cell and its component sperm cells, to the ovule (Lord and Russell 2002). We discovered an adhesion event between the pollen tube and the stylar transmitting tract in several species and have isolated the molecules from the style that cause this adhesion. Our hypothesis is that adhesion events between the pollen tube and the style facilitate tube cell movement to the ovary. Adhesion molecules are common in animal development and are involved in cell movement and differentiation but none had been described in plants. To look for the adhesion molecules in the style we developed an in vitro adhesion assay that mimics the in vivo interaction between the pollen tube and the style in lily. We used this assay to isolate the two molecules necessary for pollen tube adhesion to the stylar ECM; they are a pectic polysaccharide and a 9kD protein, SCA (stigma/stylar cysteine-rich adhesin). We are studying how these two molecules interact to cause adhesion. The two molecules are necessary together to allow for adhesion and one requirement is that they bind to one another. One approach we are taking is to selectively remove parts of the pectic polysaccharide to determine the mode of interaction between the pectin and the peptide. Another goal using several enzymes is to elucidate the essential components of the pectin in adhesion.

We are also interested in how the matrix binds the pollen tube. Antibodies to SCA localize it to the pollen tube tip when in vitro pollen tubes are grown in the presence of SCA. We are using chemical genetic screens to detect small molecules that can disrupt the adhesion event. So far we have 8 molecules that are candidate "hits". We will test these in an assay with Arabidopsis pollen and eventually do mutant screens to get to the target. This is an approach that may lead to the pollen tube partner molecule in the adhesion event.

Doing expression studies of SCA we found the stigma to have an abundance of this peptide even though the adhesion events occur only in the style in lily. We speculated that this peptide may have another role in pollination separate from the one in adhesion. Many molecules involved in adhesion in animal systems are also involved in chemotropism. A recent exciting finding is that SCA facilitates the action of a chemotropic peptide in the stigma (Kim et al., 2003). The lily stigma is large and highly secretory providing a medium for pollen germination and growth towards a central canal that is the entrance to the hollow style. We found a stigma protein fraction that worked in an in vitro chemotropism assay that mimics the stigma surface. Proteinase treatment of this prep destroys the activity. The predominant protein in this fraction is SCA but expressed SCA (Park and Lord 2003), which works in the adhesion assay, does not work in the chemotropism assay. We used LC/Mass Spec to further purify the SCA prep and found another small basic protein that is in low abundance that is the active protein in the assay. We have named this 9.8kD protein chemocyanin, the first such chemotropic peptide to be described in plants. The activity of chemocyanin is greatly enhanced by the presence of SCA in the assay so we postulate that they work together to effect directional growth of the pollen tube. Our search now is for the receptor in the pollen tube that perceives a gradient of SCA and chemocyanin and responds to it. Our hypothesis is that it somehow alters calcium channels in the pollen tube tip that would be responsible for directed growth. Our research on adhesion molecules and their role in pollen tube guidance is supported by funds from NSF, Developmental Mechanisms.

A Lily pollen tubes adhere to and grow on an in vitro stylar matrix. Stylar matrix collected from lily styles (se) is dried onto nitrocellulose membrane (nc). Adhered pollen tube (pt) tip. (Molecular Cell Biology, Lodish et al., 2004, Chapter 6)	B. Lily flowers C. Chemotropism assay using lily chemocyanin in the central well. Pollen tubes show reorientation in presence of the gradient. D. Lily: stigma, style and anthers (Kim et al., 2003)

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Current Laboratory Personnel and Projects

• Suntae Kim, Postdoctoral Researcher
• Ornusa Kamsak, Graduate Student-Plant Biology Program (Ph.D.)
• Keun Chae, Graduate Student-CMDB Program (Ph. D.)
• Shruthi Bala, Laboratory Assistant
• Michael Wong, Undergraduate Student
• Benedict Gonong, Undergraduate Student
  

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Selected Publications in Cell and Developmental Biology (Bibliography page)

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