The promise of drought-tolerant and disease-resistant barley

Image by Gerste Ähren (CC BY-SA 3.0)

Image by Gerste Ähren (CC BY-SA 3.0)

Barley is the fourth most important cereal crop in the world (behind rice, maize and wheat) and is grown in both temperate and tropical climates. It was one of the first grains to be domesticated and has a variety of uses including in the alcoholic drinks beer and whisky, as a foodstuff (especially in the Middle East) and for animal feed. Like other crops, the barley yields can be affected by many different pests and diseases, but also by adverse environmental conditions such as drought or low soil nutrients.

In July last year, I wrote about how a variety of barley called Golden Promise was genetically-modified to be more drought-tolerant (see previous post). This variety carries an extra copy of an existing barley gene—called HvSNAC1—that promotes the closure of pores (stomata) on the surface of barley leaves to reduce water loss when water is scarce (1). However, it was not known if making the plants more drought tolerant in this way could alter the ability of the plants to resist diseases caused by invading microbes.

Researchers at the John Innes Centre and SRUC studied that the ability of this variety to resist infection by several fungi that can cause diseases in barley (2). McGrann et al. found that the plants are more resistant to infection by a fungus called Ramularia collo-cygni. This fungus causes a disease called Ramularia leaf spot, a newly emerging disease that is currently affecting barley crops in Europe.

How can a single gene make plants more drought-tolerant and disease-resistant? One possibility is that the HvSNAC1 gene could promote the closure of stomata, which is the main way that the fungus can enter barley leaves. However, the experiments show that when the barley plants were treated with the fungus, the stomata of the plants carrying an extra copy of HvSNAC1 remained just as widely open as the control plants.

The symptoms of Ramularia leaf spot tend to appear late in the season when the leaves are starting to die back (senescence). Leaf senescence was delayed in the barley variety carrying an extra copy of HvSNAC1, suggesting that this may be linked to the increased resistance, but how is not clear.

It is important to note that although HvSNAC1 does increase the resistance of the barley to infection with R. collo-cygni, it does not have any effect on resistance to diseases caused by powdery mildew (Blumeria graminis f. sp. hordei), eyespot (Oculimacula yallundae) and several other fungi. However, producing a crop variety with increased resistance to even one fungal disease is still a step forward.

This research shows that it is possible to improve a crop’s tolerance for extreme environmental conditions and improve its resistance to a fungal disease at the same time.

References:

1) Al Abdallat et al. (2013) Overexpression of the transcription factor HvSNAC1 improves drought tolerance in barley (Hordeum vulgare L.). Journal of Molecular Breeding. (link above is to the freely available PDF, for closed access version on publisher’s website click here)

2) McGrann, G.R.D. et al. (2015) Contribution of the drought tolerance-related Stress-responsive NAC1 transcription factor to resistance of barley to
Ramularia leaf spot. Molecular Plant Pathology.

Advertisements

6 thoughts on “The promise of drought-tolerant and disease-resistant barley

  1. Here’s an idea (from a non-scientist so forgive the speculation) – perhaps the improved disease resistance is simply because being draught resistant means the plant doesn’t suffer the same level of stress as non-draught resistant varieties (is just healthier) and therefore more able to resist infection. The same way that exercise in humans apparently not only boosts our immune system but also means our basic defences aren’t as easily weakened by everyday stresses (rather than specific infections).

    My understanding is that scientists can detect stress in plant cells some 7-10 days before they can detect it in any visible physical change – during that time the plant becomes more vulnerable to other diseases. If the draught tolerance closes that time-frame down, the overall resistance might increase.

    Realise this is probably badly explained (and based on partial knowledge) – but hopefully you’ll understand and be able to explain why I am wrong.

    Cheers

    Huw

  2. Huw, your explanation sounds very plausible to me (another non-scientist!). Much is not understood about plant physiology but it is known that healthy, unstressed plants are less susceptible to pests and diseases in general. Thanks for the interesting article, Sarah.

  3. Thank you both for your comments. I agree that stressed plants can be more vulnerable to infections but that can’t account for what was found in this study for a couple of reasons:

    1. the barley plants were grown under normal growth conditions and so they are very unlikely to have been experiencing stress due to drought or any of the other environmental conditions. (Sorry, I probably should have mentioned this in the article!)
    2. the plants with an extra copy of HvSNAC1 were only more resistant to one fungal disease, suggesting that the role of HvSNAC1 is specific to how Ramularia infects the plant, not just a general stress response.

    HvSNAC1 is a gene that promotes the switching on of other genes. It may be that HvSNAC1 switches on genes that delay leaf senescence and just happen to do something that increases the resistance of the plants to infection. Alternatively, it is possible that the plants are more vulnerable to infection when the leaves are senescing, so the delayed leaf senescence in the plants with extra HvSNAC1 protects them from infection.

  4. Enjoyed reading that as both a barley and stomata fan! I was wondering whether you know of any research testing the nutritional content of the Golden Promise grains? Some research suggests that modifying transpiration affects the plant’s ability to take up things like iron from the soil, since the water lost through the stomata drives this process, so it’d be interesting to see if it is affected in these plants.

    • Thanks Sarah 🙂 As far as I know the only papers published on the Golden Promise over-expressing HvSNAC1 are the two listed in the references of this article. I remember that in the original paper (Al Abdallat et al 2013) they found that the yields of the barley were higher than in the normal Golden Promise but I can’t remember if they checked nutritional content of the grains.

  5. Pingback: Morsels For The Mind – 06/02/2015 › Six Incredible Things Before Breakfast

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s