Question

Describe the process of retrograde signalling and further, what molecule is believed to most frequently serve as a retrograde signal in plants?

Answer 1

Retrograde signalling is defined as the process where the feedback mechanism of some part of a cell regulates another part of the cell. Retrograde signalling can be seen in both cell biology and neuroscience domains. In the case of plants, retrograde signalling is seen in nuclear gene expression controlling process occurring in plastids. Organelle to nuclear retrograde signalling is a controversial topic for many years. In a primitive red alga, it was found that the Mg-protoporphyrin IX, which is plastid-derived, activates nuclear DNA replication through Cyclin1 accumulation. Activation of the chloroplast protein genes through retrograde signalling which is activated by light leads to nuclear gene transcription.

In case of neuroscience, the retrograde signalling is the process where the postsynaptic dendrite releases chemical messengers such as nitric oxide, released upon stimulation by the long-term potentiation (LTP) factors. These messengers proceed in a back direction to bind to the axon terminals of the presynaptic neurons. Another mechanism of retrograde signalling in neuroscience could be the alteration of synapse spanning proteins through LTP induction stimulus, which changes the conformation of these proteins in the postsynaptic cell leading to their transmission across the presynaptic cells.

In case of plants Mg-protoporphyrin IX, which is plastid-derived, is believed to be the most frequently served retrograde signal. It activates nuclear DNA replication through Cyclin1 accumulation. It prevents the degradation of Cyclin1 leading to Cyclin1 accumulation and nuclear DNA replication.