Minisymposium 20: Photomorphogenesis

Abs # 41002: Characterization of Light-Induced Chloroplast Movement in Arabidopsis

Presenter:	Luesse, Darron R, dluesse@bio.indiana.edu
Authors	Luesse, Darron R (A)   DeBlasio, Stacy R (A)   Hangarter, Roger P (A)
Affiliations:	(A): Indiana University

The optimization of photosynthesis is critical for a plant to thrive. While a plant can do little to alter the amount of light to which it is exposed, movement of chloroplasts allows alterations of the amount of light the photosynthetic machinery itself absorbs. Under low fluence rates, chloroplasts accumulate along the periclinal cell walls (top and bottom, or face position) and under high fluence rates, the chloroplasts migrate to anticlinal cell walls (sides, or profile position). It is hypothesized that chloroplasts move to the face position under low fluence rates to maximize light capture, and to the profile position under high fluence rates to avoid photodamage. Although the exact mechanism of movement is not yet understood, treatment with cytochalasin D, an inhibitor of actin polymerization, inhibits the response. The goal of this research is to better understand the mechanisms that control light-induced chloroplast movement. A mutant screen designed to isolate lines with altered chloroplast movement has been effective. One gene identified in this screen, PMI2 (Plastid Movement Impaired) has been cloned. Under low light conditions, pmi2 displays normal chloroplast movement. However, under intermediate and intense light conditions, the response is severely attenuated, producing a low-light response under light conditions that normally cause movement to the profile position. The function of PMI2 is currently unknown. The bulk of the protein consists of coiled-coil domains in three conserved regions. The C-terminus contains a putative nuclear localization signal and a P-Loop. BLAST analysis indicates low homology to both the tail of myosin and to Smc1, as well as 57% amino-acid identity to another gene in Arabidopsis. Utilization of a GFP::mouse talin construct that highlights filamentous actin, time-lapse analyses, and other microscopic techniques that provide visual information about the mechanism of movement will be shown.