Title : The movement of Chlamydomonas reinhardtii in response to light is mediated by abscisic acid
Abstract:
The phytohormone abscisic acid (ABA) regulates plant responses to various abiotic stresses and diurnal rhythms that alter their water status. Sequencing of the Chlamydomonas reihardtii genome has shown that this flagellate, motile, freshwater, photosynthetic green alga is also capable of synthesising and responding to ABA. Algae were sampled at different time points over 24h in a cyclic 16h photoperiod and were treated with or without 50 µM ABA in either the light or dark and their position in the water column was monitored by measuring the A750 at different depths. The actual position attained by the algae in the water column correlated with the time at which they were sampled in the cycle, but in general, ABA induced upward movement of the algae.
Plants possess a number of glycine rich RNA-binding proteins (GRPs) that appear to be involved in stress responses that are regulated by ABA. Chlamydomonas appears to possess only a single GRP gene which appears to encode a flagellum-associated protein, which we have termed CrGRP1, which may be involved in regulating its movement. Expression of CGRP1 was assessed during the algal movement experiments described above and appeared to decline to the greatest extent when ABA induced the greatest upward movement of the algae.
The suggestion is that ABA regulates the movement of Chlamydomonas in the water column in order to position itself to optimise photosynthesis and that CrGRP1 negatively regulates the ABA-induced upward movement of the algae, presumably by binding mRNAs required for this response.
Abscisic acid (ABA)- glycine rich RNA-binding proteins (GRPs)- Chlamydomonas reinhardtii
