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.
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.