Published in Lab Times 03-2011.
Animals and plants have more things in common than you might think, finds a Portuguese research team.
The retention of certain ‘successful’ mechanisms and fundamental processes across species has been a hallmark of evolution. A recent connotation to this is the finding by José Feijó and colleagues at Instituto Gulbenkian de Ciência, Lisbon, of a novel but evolutionarily reiterated pathway in the control of pollen tube growth (Science, 2011 Mar 17).
Given that cytosolic calcium oscillations among other factors affect pollen tube growth in vitro, what continued to intrigue biologists was the nature of regulation of the calcium ion (Ca2+) fluxes. In their studies on tobacco and Arabidopsis, the Feijó group have identified glutamate receptor-like (GLRs) calcium channels at the growing tip of the pollen tube that regulate calcium influx and hence, cellular Ca2+ concentrations. Out of the six different GLRs found in Arabidopsis pollen grains, they were able to pin down on two GLR genes, mutants of which produced low counts of seeds and deformed pollen tubes suggestive of partial male sterility.
At the molecular level, they were able to show that a rare amino acid, D-serine (D-Ser) increased Ca2+-oscillation amplitudes and is, in fact, crucial in eliciting a concentration-dependent bi-phasic response upon stimulation of GLRs while antagonists to the latter served to inhibit oscillation amplitudes. The story was neatly finished with their observation that D-Ser is made by an enzyme that is exclusively expressed in the pistil, the female reproductive organ.
Animal GLRs have been associated with fast excitatory neurotransmission in the central nervous system and hold prominent implications in neurologic disorders, including epilepsy and ischemic brain damage and more speculatively, in neurodegenerative disorders. Besides a role in neuronal development, these ionotropic receptors have major roles in cognition viz. learning and memory.
D-Ser, a coagonist of GLRs is expressed primarily in the brain and functions as an endogenous ligand for the GLR-mediated Ca2+ flux. Now, the latest finding by the Feijó group has only increased the repertoire of roles of GLRs. Besides, it represents a classic case of how cell-cell communication processes involving analogous genes are conserved across plant and animal species.
Photo: Arabidopsis thaliana by Rea via Creative Commons License