Lecture 9 Pt 1.Another look at organism-organism interactions. Pt 2.The lessons of the SH for biochemical evolution

Organism – organism interactions What lessons might the Screening Hypothesis contain for those studying such interactions? One can assume no function for any one NP Biological activity that is found cannot be assumed to be important or relevant Inducibility – what is it? Why has it evolved?

One can assume no function for any NP Gas chromatograph trace shows the many volatile NPs from a corn plant The response of one insect olfaction cell to those chemicals Time

Biological activity that is found cannot be assumed to be important or relevant Which of these chemicals is made because the plants gains fitness by making that NP? The anti-cancer drug vincristin? The anti-cancer drug taxol? The stimulant caffeine? Every one of the furanocoumarin family? All chemicals with antifungal properties? More likely that the organisms making these NPs gain fitness from the overall ability to make many diverse chemicals, a very few of which enhance the fitness – quite possibly chemicals not yet found, characterised or known? Mammals gain fitness by having an immune system not by having a particular antibody?

Inducibility – what is it? Why has it evolved? Inducible defenses – where the rate of development of damage is slow, there are resource benefits to be had if the plant only makes defensive chemicals after the attack has started. Phytoalexin model illustrates the paradigm. Examples are known of the systemic induction of chemicals – where the part of the plant initially attacked sends a “signal” to adjacent areas to induce defenses there before those areas are attacked. Thousands of papers have been published on this topic. It is a subject of great commercial interest. But the story has become less simple …..

Inducibility – what is it? Why has it evolved? Cost saving – only make a defence when needed? But Agrawal & Karban give some alternative theories Making the plant harder to find Reducing the rate of development of resistance to defensive chemical Reduce autotoxicity Reduces chances of negative side effects and many more ……..

Inducibility – what is it? Why has it evolved? “Cross talk” As people began to investigate the stimuli (“elicitors”) evoking defense reactions in plants, and in particular after the developed methods to analyse changes in gene expression, it became clear that the various pathways interacted. This is termed “cross talk”.

A -> B A -> B -> C -> Insecticide? A -> B -> C -> Fungicide? A -> B -> C -> Attractive scent? A -> B -> C -> Colour? What can the Screening Hypothesis add to this debate about cross talk? How are appropriate regulatory systems evolved when pathways can serve multiple roles?

Is it necessary to duplicate the control processes at every step?

How are appropriate regulatory systems evolved when pathways can serve multiple roles? Could it be that most NP pathways have several common control points near the start which allow many stimuli to upregulate them? Thus insect or fungal attack might turn a pathway but which product, if any, is important could be unclear.

If cross-talk is inevitable, inducibility becomes a poor predictor of function Cross-talk is the term used to describe the fact that certain control systems seem to interact. A particular gene turned on by fungal attack might also turned on by insect attack. Cross talk is very fashionable but was without explanation. Maybe we now have an explanation. Inducibility has often been an important part of the evidence produced in favour of any one NP playing a specific role in a particular circumstance.

Organism – organism interactions Summary Nearly all such studies of the role of NPs in the organisms that make them have been conducted using the chemical co-evolution model to guide the design and interpreation of the experiments. The SH suggests that scrutiny will now be needed. Whether greater progress is made in future …..

Vermouth is a fortified wine flavored with NPs in recipes that are closely- guarded trade secrets. The inventor of vermouth, Antonio Benedetto Carpano from Turin, Italy, chose this name in 1786 because he was inspired by a German wine fortified with wormwood, an herb most famously used in distilling absinthe. (Wikipedia)

Pt 2 – Bichemical evolution. The bigger picture

The Screening Hypothesis is now part of a bigger model

Lipids The Screening Hypothesis is now part of a bigger model

Colours – carotenoids, anthocyanins The Screening Hypothesis is now part of a bigger model

Matrix pathways with low substrate specificity enzymes found making chemicals with useful physicochemical properties. Reservoir for more chemical diversity?

The Screening Hypothesis is now part of a bigger model

Terms such as primary metabolism, secondary metabolism and even NP are not really meaningful classifications.

Thanks Clive Jones  How science works. One simple idea - potent biological activity is rare - led to renewed debate. The debate did not need:  amazing new instruments  expensive new techniques  a huge input of human resources Just a little knowledge, some imagination, simple logic and thought. The knowledge was not even new - it had been widely available for decades. Teaching you to think creatively is what we should have been doing over the last 3 years.... have you thought about that.....

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