This SciShow video is sponsored by Helix Sleep, which makes premium mattresses that  are customized to fit your needs.

Click on the link below or go  to helixsleep.com/scishow for up to $200 off your Helix Sleep  mattress plus two free pillows! [♪ INTRO] Our microbiomes have become super  famous in the last several years. We’ve learned that a world of  tiny organisms living inside of us helps us digest food, produce vitamins,  and regulate our immune system.

But humans aren’t the only life form  playing host to entire ecosystems. Other animals have their own complex  microbiomes, and amazingly, so do plants. And these tiny microbes may play a surprisingly large role in plants’ survival and evolution.

Plant microbiomes are partly made up of  fungi and bacteria called endophytes, which live at least part of  their lives inside plants. Unlike the microbes that cause mildew and  root rot, these don’t harm their hosts. So plants and endophytes get along just fine.

In some cases, a plant and endophyte  will spend their entire lives together, almost as if they were a single organism. For instance, obligate endophytes  may actually start out in the seed of their host plant, along with all the  genetic information for a new, baby plant. So they’re literally with their  host plant before it even exists.

Then, as the seed grows into a plant, they feed on its nutrients and take in its water. The plant also protects them from dangerous  UV light and extreme temperatures. And safe inside the plant,  endophytes don’t have to compete for resources with other microorganisms.

All this doesn’t cost the plant much,  so it continues to grow healthily. Meanwhile, the endophytes multiply and spread, colonizing the leaves and tips of the  shoot where flowers will eventually bloom. That way, they get incorporated into the  egg, then the embryo, and eventually, a seed, ready to start a new  generation of plant-microbe friendship.

But not all endophytes spend  their whole lives in a plant. Others can live on their own just fine, but  they’ve evolved to thrive inside plants. These so-called facultative  endophytes live outside a plant for part of their life cycle, often  in the soil or even in an insect.

But they’ll seize any opportunity  to hop onboard a plant. For instance, if they come into contact  with the natural cracks in a plant’s roots, they’ll make their way in  and colonize the whole thing. Meanwhile, passive endophytes never  go looking to colonize a plant at all, but sometimes they’ll still  end up making a home there.

Like, if some bacteria and fungi in  the soil encounter some open wounds on a plant’s roots, they might just settle in. But since these microbes aren’t  specialized for living inside plants, they never actually become symbiotic. Endophytes don’t just reap the  benefits of living in a plant, though; many actually give a lot back.

Some of them secrete chemicals that protect a plant from herbivores and harmful invaders. Because, after all, the plant is their home,  so it’s their best interest to protect it. Some endophytes also regulate  their host plants’ pores.

For instance, when the weather is  hot and dry, endophytes can help keep pores closed so the plant loses  less water, protecting it from drought. These pores also let carbon  dioxide in and oxygen out. Since these are inputs and  outputs of photosynthesis, regulating them can make a plant more  efficient at converting sunlight into fuel.

And finally, host plants can  also count on certain endophytes to help them take in nutrients.   When these microbes colonize a root  system, they increase the roots’ surface area, which lets the plant take  up more water and nutrients from the soil. Once inside a plant, endophytes can  also break down nitrogen in the air and turn it into other compounds the plant can use. On top of all that, some will  secrete hormones that can make their host more efficient at absorbing nutrients.

With all these extra resources, a  plant can grow bigger and produce more fruits and flowers that spread seeds. And sometimes, the endophytes in a  plant’s seed might convert enough nitrogen into nutrients to help its host to sprout in  the first place, even in harsh conditions. So, these tiny microbes can be  incredibly important to plants’ survival.

And plants and endophytes seem to have been working together for a long, long time. Fossil records suggest that fungi may  have colonized the very first plants to live on land, 400 million years ago. In fact, they might have actually  helped plants evolve to survive here.

A paper in 2003 found that there’s  at least one type of endophyte in every single plant species ever discovered. But they haven’t just lived  together all these years. It seems that plants and their endophytes  have actually evolved together.

What’s amazing about that is that, historically,  scientists thought natural selection was pretty simple: Individual organisms  with the best genes were the most likely to survive and pass on their DNA. And they thought this is what  drove the evolution of a species. But when researchers discovered endophytes, they realized that may not be  the whole story for plants.

Now, scientists think that natural selection acts on a plant species plus its microbiome. So, in survival of the fittest, fitness  is determined by the genes of a plant and the genes of all the microbes  that call that plant home… almost as if the whole ecosystem  were a single organism. At first, the relationship between a plant  and an endophyte might seem like your run-of-the-mill symbiotic relationship.

But plant microbiomes are incredibly  complex, just like humans’. And what we’ve learned so far shows  that the relationships between plants and their microbes are profound. They may not affect just a single  plant, but a species as a whole.

Which is a pretty major achievement  for a microscopic world. And just like microbes are unexpectedly  important in a plant’s life, your mattress may be unexpectedly  important to your life. Which is why Helix customizes their mattresses and bedding to suit your particular sleep needs.

To find the right fit for you,  you can take their sleep quiz. Like, I prefer a firm  mattress and sleep on my side, so they recommended their Helix Twilight Mattress. And once you’ve found the right mattress for you, let Helix ship it to your door  for free anywhere in the US.

Then you get 100 nights to try it out  in your home and make sure you like it. If you don't, they'll pick it  up for you with a full refund. And if you do, you still get a 10-year warranty.

When you’re ready to buy,  Helix makes it easy to pay with different financing options  and flexible payment plans. And if you click on the link below  or go to helixsleep.com/scishow, you can get up to $200 off your Helix  Sleep mattress plus two free pillows! Thank you to Helix for supporting this  SciShow video and thank you for watching! [♪ OUTRO]