/* */ Rosa Rubicondior: Malevolent Designer News - How a Bacterium Turns Plants Into Zombies

Monday, 20 September 2021

Malevolent Designer News - How a Bacterium Turns Plants Into Zombies

Lime witches broom, induced by Phytoplasma
The microbial molecule that turns plants into zombies | John Innes Centre

Parasites that turn their hosts into zombies that serve only the needs of the parasite, are by no means uncommon in nature. In fact, I include several examples in my popular, illustrated book, The Malevolent Designer: Why Nature's God is not Good. To the perpetual embarrassment of Creationists who like to pretend that their putative designer god is one and the same as the supposed god of love in the Christian Bible, they betray the fiendishly evil, amoral mind of anything that could have consciously and intentionally designed such relationships.

And now we have one more to add to the long, sorry list.

This example of the malevolent nastiness of any mind that designed such a thing, is that of the genus of bacteria known as the Phytoplasma, which infect various plants and take control of their development, often making them unable to reproduce and simultaneously prolonging their life, to the benefit only of the bacteria. These bacteria use insect vectors, so are spread by, for example, aphids. They are responsible for the familiar 'witches brooms' seen in trees such as birch, where there is a proliferation of twigs and shoots with few, if any, reproductive structures.

A research team working at The John Innes Centre, Norwich, Norfolk, UK has now discovered how exactly they pull off this trick. From the John Innes Centre press release accompanying the open access publication of the team's findings being in Cell:
A newly discovered manipulation mechanism used by parasitic bacteria to slow down plant aging, may offer new ways to protect disease-threatened food crops. Parasites manipulate the organisms they live off to suit their needs, sometimes in drastic ways. When under the spell of a parasite, some plants undergo such extensive changes that they are described as “zombies”. They stop reproducing and serve only as a habitat and host for the parasitic pathogens. Until now, there’s been little understanding of how this happens on a molecular and mechanistic level.

Phytoplasmas are a spectacular example of how the reach of genes can extend beyond the organisms to impact surrounding environments. Our findings cast new light on a molecular mechanism behind this extended phenotype in a way that could help solve a major problem for food production. We highlight a promising strategy for engineering plants to achieve a level of durable resistance of crops to phytoplasmas.

Professor Saskia Hogenhout
John Inness Center
Norwich, Norfolk, UK
Research from the Hogenhout group at the John Innes Centre and collaborators published in Cell, has identified a manipulation molecule produced by Phytoplasma bacteria to hijack plant development. When inside a plant, this protein causes key growth regulators to be broken down, triggering abnormal growth.

Phytoplasma bacteria belong to a group of microbes that are notorious for their ability to reprogramme the development of their host plants. This group of bacteria are often responsible for the ‘witches’ brooms’ seen in trees, where an excessive number of branches grow close together. These bushy outgrowths are the result of the plant being stuck in a vegetative “zombie” state, unable to reproduce and therefore progress to a ‘forever young’ status.

Phytoplasma bacteria can also cause devastating crop disease, such as Aster Yellows which causes significant yield losses in both grain and leaf crops like lettuce, carrots, and cereals…

The new findings show how the bacterial protein known as SAP05 manipulates plants by taking advantage of some of the host’s own molecular machinery. This machinery, called the proteasome, usually breaks down proteins that are no longer needed inside plant cells. SAP05 hijacks this process, causing plant proteins that are important in regulating growth and development, to effectively be thrown in a molecular recycling centre.

Without these proteins, the plant’s development is reprogrammed to favour the bacteria, triggering the growth of multiple vegetative shoots and tissues and putting the pause on the plant ageing.
Because the developmental proteins to which SAP05 binds in plant cells and the proteasomes, are also found in animal cells, where they serve the same purpose, one of the puzzles was why the bacterium doesn't affect the insect vectors the way it affects plants. The team found that the insect version of the proteins differs enough to prevent SAP05 binding. In particular the insect proteasome differs by just two amino acids from the proteasome of plants - and that represents an opportunity to develop a prevention for these infections which can devastate crops. When the two amino acids in the plant proteasome were replaced by the two found in insects, the plant was made resistant to the bacteria.
…this investigation allowed the team to pinpoint just two amino acids in the proteasome unit that are needed to interact with SAP05. Their research showed that if the plant proteins are switched to have the two amino acids found in the insect protein instead, they are no longer degraded by SAP05, preventing the ‘witches’ broom’ abnormal growth. This finding offers the possibility of tweaking just these two amino acids in crops, for example using gene-editing technologies, to provide durable resilience to phytoplasmas and the effects of SAP05.
Graphical Abstract
The findings are published, open access, in Cell:
Summary

Certain obligate parasites induce complex and substantial phenotypic changes in their hosts in ways that favor their transmission to other trophic levels. However, the mechanisms underlying these changes remain largely unknown. Here we demonstrate how SAP05 protein effectors from insect-vectored plant pathogenic phytoplasmas take control of several plant developmental processes. These effectors simultaneously prolong the host lifespan and induce witches’ broom-like proliferations of leaf and sterile shoots, organs colonized by phytoplasmas and vectors. SAP05 acts by mediating the concurrent degradation of SPL and GATA developmental regulators via a process that relies on hijacking the plant ubiquitin receptor RPN10 independent of substrate ubiquitination. RPN10 is highly conserved among eukaryotes, but SAP05 does not bind insect vector RPN10. A two-amino-acid substitution within plant RPN10 generates a functional variant that is resistant to SAP05 activities. Therefore, one effector protein enables obligate parasitic phytoplasmas to induce a plethora of developmental phenotypes in their hosts.

This entire system is of course, for the sole 'purpose' of making more Phytoplasma bacteria. If we accept for the moment the Creationist argument that it must be designed for a purpose, the only discernible purpose for these bacteria is to parasitise and zombify plants in order to make more bacteria.

Creationists regard this as evidence of a supreme design ability, forgetting that one of the hallmarks of good design, in addition to minimal complexity, is a clear purpose for the design. Imagine a real designer designing a massively complex machine which does nothing other than make copies of itself and which goes around consuming other machines in order to get the raw materials it needs. How on Earth could that be regarded as the work of an intelligent person, and not a malevolent vandal who destroys things for the sake of it?


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