Precision insecticide

Precision insecticide

Fields full of crops are an all you can eat buffet for many insects. They eat the plants. Not something a farmer wishes, as it lowers the yield. The most effective method: killing all the insects with insecticides. Although, this is also not something we like to do. A dilemma for the farmer. How to only kill the harmful insects?

The ideal: only killing the insect that eats the plant, the ones that are harmful. With this idea, scientist went on searching. Searching for precision insecticide. They bumped into a method that organisms already use. The turning off genes using interference-RNA.

Interference-RNA are small pieces of RNA that match a gene. When a gene is turned on, the cell makes an RNA-copy of it, which the cell uses in the process of making the protein that the gene codes for. But when an RNA-copy comes across matching interference-RNA, then they bind together. A sign for the cell to cut the RNA-copy in small pieces, not making the protein. This can switch off a specific gene, as the small piece of RNA only binds RNA that precisely matches. If the small piece of RNA matches a gene that is essential for an organism, the organism dies. A perfect method to only kill those insects that harm the plants.

Lots of insects nibble on leaves. To kill these, using the interference-RNA method, just spraying the small pieces of RNA on the leaves is enough. A special challenge are the sap-sucking insects. These insects, like vampires, drink the sap from the veins in the plant. To kill the sap-sucking insects, the small pieces of RNA need end up in the veins, so the sap-sucking insects will drink them. Australian researchers took on this challenge.

First, they designed small pieces of RNA so that they would only kill the sap-sucking whitefly. This they tested by feeding the interference-RNA to whiteflies, aphids and bees. While the whiteflies died after eating these small pieces of RNA, the closely related aphids and bees stayed alive.

Next, the researchers attached the small pieces of RNA to so called BioClay particles, miniscule grains made of magnesium and iron. The effect of this was that the RNA stayed longer intact. The researchers sprayed the BioClay attached RNA pieces together with a helping substance on the leaves of cotton plants. The helping substance was needed so the RNA pieces could penetrate the water repelling layer on the surface of the leaves. This gives the RNA pieces a chance to get inside the leaf. This they did.

The researchers observed that the small pieces of RNA got into the leave and into the veins. Whiteflies that drank the sap of these plant died more often than whiteflies that drank sap of the control plants. But not only that also the eggs and nymphs of whiteflies on plants treated with the BioClay coupled RNA pieces died more often than those on control plants.

Interference-RNA does appear a precise way to deal with insects that eat our crops. With it you can precisely kill, not only nibbling insects, but also sap-sucking insects. A possible way out for a farmer that prefers to kill only the insects that eat his crops.

Literature

Ritesh G. Jain, Stephen J. Fletcher, Narelle Manzie , Karl E. Robinson, Peng Li, Elvin Lu, Christopher A. Brosnan, Zhi Ping Xuand Neena Mitter (2022) Foliar application of clay-delivered RNA interference for whitefly control. Nature Plants, VOL 8, 535–548

How light gets to the root

How light gets to the root

The waiting starts, after sowing seeds, for the first leaves to stick out of the ground. A just germinated plant, that found its way in the dark to the light. In the dark the main way of growing for a plant is through stretching its cells. Not by making new cells. This changes the moment the leaves stick out of the ground. Then light tells the cells of the plant: Start dividing. Start photosynthesis. Start using energy. But how does light tell this to all the cells of the plant, not only those in the leaf, but also those in the root?

The plant hormone auxin has a part in this. Auxin has more or less a role in everything in the plant. But one of its important tasks is the promotion of cell division. In a seedling that is still searching for the light, auxin is located mostly at the top of the stem. But as soon as the plant finds light, auxin moves to the tip of the root. Here cell division starts in the meristem, the root grows.

But this does not happen in a mutant, kai2, that had trouble with the transition from dark to light. The order from light: Start growing, use energy! Does not come through correctly. The tip of the root does not start growing, the seedling makes lots of side-roots instead. Auxin, so noticed the researchers, was not in the tip of the root but at the top, there were the root meets the stem. Here auxin accumulates, and does what auxin does best, stimulate cell division.

With use of auxin transferring PIN-channels, the plant is getting auxin in the right spot. At least when everything works as it should. Not so much in the kai2 mutant. The researchers had a look at the PIN-channels in kai2. In the dark, by just germinated seedlings, the PIN-channels in kai2 are at the same spot as in normal plants. But, whereby normal plants the PIN-channels quickly get to their new spot, those of kai2 lag behind. Auxin can not get quickly to the right place.

This shows that using KAI2, light can tell the whole plant ‘Start dividing, start photosynthesis, start using energy’. KAI2 in turn gives an order to the PIN-channels to change places. Giving auxin the chance to get to the right spot to stimulate cell division. Now there is a start of the answer how lights gets to the root.

Literature

Hamon-Josse, M., Villaécija-Aguilar, J.A., Ljung, K., Leyser, O., Gutjahr, C. and Bennett, T. (2022) KAI2 regulates seedling development by mediating light-induced remodelling of auxin transport. New Phytol. https://doi.org/10.1111/nph.18110

Hoe licht de wortels bereikt

Hoe licht de wortels bereikt

Na het zaaien van zaadjes begint het wachten tot het eerste blaadjes boven de grond uit steken. Een net ontkiemt plantje, dat zich in het donker de weg naar het licht gevonden heeft. Tot dit licht gevonden is groeit een plant door z’n cellen uit te strekken. Er komen nog geen nieuwe cellen bij. Dit verandert wanneer het z’n blaadjes boven de grond steekt. Licht vertelt de cellen in de plant: Begin met delen. Begin met fotosynthese. Begin met energie verbruiken. Maar hoe vertelt licht dit aan alle cellen van de plant, niet alleen die in het blad maar ook die in de wortels?

Het plant hormoon auxin heft hier een rol. Auxin heeft eigenlijk overal wel een vinger in de pap. Maar een van de belangrijkste taken van auxin is het aanmoedigen van celdelingen. In een zaailing dat nog opzoek is naar licht zit auxin voornamelijk in het bovenste stukje van de steel. Maar zodra licht is gevonden verplaatst auxin naar het puntje van de wortel. Daar beginnen dan de meristem cellen te delen, de wortel groeit.

Dit gebeurt niet in een mutant, kai2, die moeite had met de overgang van donker naar licht. Het bevel van licht: Ga groeien, gebruik energie! Komt niet helemaal goed door. In plaats van te gaan groeien aan de tip van de wortel maakte de plant heel veel zij wortels. Auxin, zo ontdekte onderzoekers, zit hier niet in de tip van de wortel maar aan de bovenkant, daar waar de stem en wortel samenkomen. Hier is een ophoping van auxin, die daar gewoon z’n ding doet: het stimuleren van celdelingen.

De plant zorgt ervoor dat auxin op de juiste plek komt met help van auxin doorlatende PIN-kanaaltjes. Dat is wanneer alles gaat zoals het moet gaan. Dit was niet het geval in de kai2 mutant. De onderzoekers keken daarom wat de PIN-kanaaltjes doen in kai2. In het donker, bij net ontkiemde zaailingen, zitten de PIN-kanaaltjes in kai2 nog op dezelfde plek als in de gewone plant. Maar waar bij het vinden van licht de PIN-kanaaltjes in de gewone plant snel van plek veranderen, doen die van de kai2 plant dat heel langzaam. Auxin kan dus niet snel op de juiste plek komen.

Dit laat zien dat licht aan de hele plant kan vertellen ‘begin met delen, begin met fotosynthese, begin met energie verbruiken’ via KAI2. KAI2 draagt vervolgens de PIN-kanaaltjes op om snel van plek te veranderen. Wat ervoor zorgt dat auxin op de juiste plek komt om celdelingen te stimuleren. Er is een begin op het antwoord hoe licht de wortels bereikt.

Literatuur

Hamon-Josse, M., Villaécija-Aguilar, J.A., Ljung, K., Leyser, O., Gutjahr, C. and Bennett, T. (2022) KAI2 regulates seedling development by mediating light-induced remodelling of auxin transport. New Phytol. https://doi.org/10.1111/nph.18110

A good place to land

A good place to land

In an impulse you pick a fluffy head of a dandelion, breath in and blow the stem clear. Hundreds fluffy seeds fill the air. On their way to find a place for growing into a new dandelion. How do those seed know the best place?

When you look up close at a dandelion seed you will see a stick, with at the top a bit of fluff. This fluff keeps the seed in the air. Researchers from United Kingdom and France found out that in a humid environment this fluff is less fluffy. The hairs of the fluff come together, closing. The seed lands on the ground, ready to quickly germinate in this humid environment.

Zoom in further, to where the stick meets the fluff. You will see a flat top, with all around hairs attached to the side. Sticking out in all directions, right up, but mainly to the side. A fluffy ball of fluff. Researchers placed a fluffy seed in a humid environment. They noticed the top of the stick absorbing water. Making it swell. The flat top was rounding upwards. More hairs are sticking up. The fluff is not fluffy anymore.

To swell like that, to make the hairs stick straight up, this is an art. For this, so the researchers found out, the plant uses different tissue types. There is the vascular tissue, that does not absorb much water. But also, cortex tissue, died off tissue from the flower, and the tissue with the fluffy hairs attached. Each absorbing different amounts of water, varying in how much they swell. And because they are all connected, change shape, when swelling. This makes the hairs to stick up straight.

You are picking another fluffy head, blow it clear, and watch the hundreds of fluffy seeds go. Searching for a fresh start. Searching for water. So, they can then fall to the ground, and grow into a yellow dandelion.

Literature

Madeleine Seale, Oleksandr Zhdanov, Cathal Cummins, Erika Kroll, Mike Blatt, Hossein Zare-Behtash, Angela Busse, Enrico Mastropaolo, Ignazio Maria Viola, and Naomi Nakayama (2020) Informed dispersal of the dandelion. bioRxiv 542696; doi: https://doi.org/10.1101/542696

Madeleine Seale, Annamaria Kiss, Simone Bovio, Ignazio Maria Viola, Enrico Mastropaolo, Arezki Boudaoud and Naomi Nakayama (2022) Dandelion pappus morphing is actuated by radially patterned material swelling. Nat Commun 13, 2498; doi: https://doi.org/10.1038/s41467-022-30245-3