Poster: Tropisms

Abs # 396: Molecular Characterization of the Chloroplast Movement Mutant pmi1

Presenter:	DeBlasio, Stacy L, sdeblasi@bio.indiana.edu
Authors	DeBlasio, Stacy L (A)   Hangarter, Roger  (A)
Affiliations:	(A): Indiana University

In higher plants like Arabidopsis, light-dependent chloroplast movements are induced by blue light and results in two distinct arrangements. Under low light, chloroplasts migrate to the periclinal cell walls, perpendicular to the direction of light. This orientation has been suggested to optimize absorption by exposing more of the chloroplast surface to the light. In high light, chloroplasts become positioned along the anticlinal walls, parallel to the incoming light. This response is hypothesized to be a protective measure, reducing chloroplast exposure to light intensities that are damaging to the photosynthetic machinery. To identify components of the pathway, we have developed a novel screening procedure and have isolated several Arabidopsis mutants displaying altered chloroplast movements. The pmi1 mutant exhibits severely attenuated chloroplast movements under all fluence rates of light suggesting that it is a necessary component for both the low and high-light-dependant chloroplast movement signaling pathways. Bright-field images of cross-sectioned pmi1 leaves revealed that under all light conditions chloroplasts in the mutant seemed to be randomly distributed around the cells indicating that pmi1 is a novel chloroplast movement mutant not related to the chup1 mutant. Using various molecular techniques such as PCR based mapping and Agrobacterium mediated transformation, we were able to determine that the pmi1 mutant contains a single point mutation that changes an ARG residue into a stop codon. The gene encodes a plant specific protein of unknown function that is highly conserved among angiosperms. Sequence analysis of the protein suggests that it may be involved in signal transduction most likely through protein-protein interactions.