Elena Bray Speth

Subcellular Localization and Functional Analysis of the Arabidopsis GTPase RabE

Membrane trafficking plays a fundamental role in eukaryotic cell biology. Of the numerous known or predicted protein components of the plant cell trafficking system, only a relatively small subset have been characterized with respect to their biological roles in plant growth, development, and response to stresses. In this study, we investigated the subcellular localization and function of an Arabidopsis (Arabidopsis thaliana) small GTPase belonging to the RabE family. RabE proteins are phylogenetically related to well-characterized regulators of polarized vesicle transport from the Golgi apparatus to the plasma membrane in animal and yeast cells. The RabE family of GTPases has also been proposed to be a putative host target of AvrPto, an effector protein produced by the plant pathogen Pseudomonas syringae, based on yeast two-hybrid analysis. We generated transgenic Arabidopsis plants that constitutively expressed one of the five RabE proteins (RabE1d) fused to green fluorescent protein (GFP). GFP-RabE1d and endogenous RabE proteins were found to be associated with the Golgi apparatus and the plasma membrane in Arabidopsis leaf cells. RabE down-regulation, due to cosuppression in transgenic plants, resulted in drastically altered leaf morphology and reduced plant size, providing experimental evidence for an important role of RabE GTPases in regulating plant growth. RabE down-regulation did not affect plant susceptibility to pathogenic P. syringae bacteria; conversely, expression of the constitutively active RabE1d-Q74L enhanced plant defenses, conferring resistance to P. syringae infection.

Enhancement of vitamin E production in sunflower cell cultures

The most biologically active component of vitamin E, α-tocopherol, is synthesized in its most effective stereoisomeric form only by photosynthetic organisms. Using sunflower cell cultures, a suitable in vitro production system of natural α-tocopherol was established. The most efficient medium was found to be MS basal medium with naphthaleneacetic acid and 6-benzylaminopurine with the addition of casaminoacids and myo-inositol. Culture feeding experiments using biosynthetic precursors showed that α-tocopherol production improved by 30% when homogentisic acid was used. Interestingly, time-course experiments with sunflower suspension cultures showed a possible increase of 78% in α-tocopherol production when using cultures of longer subculture intervals. Compared to the starting plant tissue, an overall 100% increase of α-tocopherol was reached by these sunflower cell cultures.

Using Avida-ED for Teaching and Learning About Evolution in Undergraduate Introductory Biology Courses

Evolution is a complex subject that requires knowledge of basic biological concepts and the ability to connect them across multiple scales of time, space, and biological organization. Avida-ED is a digital evolution educational software environment designed for teaching and learning about evolution and the nature of science in undergraduate biology courses. This study describes our backward design approach to developing an instructional activity using Avida-ED for teaching and learning about evolution in a large-enrollment introductory biology course. Using multiple assessment instruments, we measured student knowledge and understanding of key principles of natural selection before and after instruction on evolution (including the Avida-ED activity). Assessment analysis revealed significant post-instruction learning gains, although certain evolutionary principles (most notably those including genetics concepts, such as the genetic origin of variation) remained particularly difficult for students, even after instruction. Students, however, demonstrated a good grasp of the genetic component of the evolutionary process in the context of a problem on Avida-ED. We propose that: (a) deep understanding of evolution requires complex systems thinking skills, such as connecting concepts across multiple levels of biological organization, and (b) well designed use of Avida-ED holds the potential to help learners build a meaningful and transferable understanding of the evolutionary process.

Introductory Biology Students’ Conceptual Models and Explanations of the Origin of Variation

Introductory biology students struggle to incorporate the molecular genetic origin of variation in their evolutionary reasoning framework. Meaningful learning of this concept may require 1) multiple cycles of instruction, assessment, and feedback; and 2) assessment forms, such as conceptual models, that promote and reveal mechanistic and causal reasoning.

How Should I Study for the Exam? Self-Regulated Learning Strategies and Achievement in Introductory Biology

Within the context of a large-enrollment, introductory biology course, this study identifies which self-regulated learning strategies that students reported using are associated with higher exam grades and with improvement in exam grades early in the course.