Rice is the most important crop ever cultivated by mankind. It has fed millions of people over millennia and has remained a staple food source for a majority of the world. The two most populous countries in the world by far, China and India, have had rice as a main product in their cuisine for hundreds of years. The former is both the largest producer of rice for the food market and the largest consumer and importer of rice in the world.[1]
With those stats, it comes as no surprise that rice farming and high rice yields is a big business and one that farmers are constantly looking to innovate in, in order to be able to produce better and better rice. There is one large hindrance, however, that has plagued rice farmers practically since the beginning. A bacterium called Xanthomonas oryzae pv. Oryzae, which causes bacterial blight in rice and has ruined many a rice crop in that same time frame. Out of all the constraints on improved rice production, bacterial blight is likely the largest concern.[2]
This obstacle has not proven to be an ignored one though, as research into giving rice crops blight resistance has been a focus of biotechnology from its early years. Back when the methods of gene transference were gold particle bombardment with a coating of the desired gene. One of the first attempt to invoke blight resistance in a rice breed was in 1998 with the IR72 variety. Even then, the results seemed immediately positive and accomplishable.[3]
It did not take long for China to get in on the action, as everyone assumed they would with what was at stake for them in rice production. By 2000, Chinese scientists had experimented with transferring the gene into not just one Chinese rice variety, but five, and enough specimens were used for them to be able to set up 110 separate lines of rice breeds. They were successful in most of the lines as well, with research continuing into incorporating the resistance into hybrid rice lines that produce higher yields.[4]
The Xa21 gene, named after the Xanthomonas genus it fights, is not only useful in rice, it should be noted. The bacterium has multiple different species that affect many different crops. As an example, the Xanthomonas campestris pv. Musacearum species causes one of the two most deadly diseases in bananas, banana Xanthomonas wilt. Being a common food source in African nations, finding a way to defend banana crops against such a disease has also been a focus for biotech researchers, with significant progress in transferring and expressing the Xa21 gene occurring in 2014. The study also transferred the rice pattern-recognition receptor (PRR) and showed that this receptor for activating and aiming the gene can be fortunately transferred to other crops as well.[5]
The latter result is an important one, as it is the receptor that properly detects Xanthomonas attack on the plant and activates the gene to combat it. Unfortunately, most plant species do not have a copy of the receptor on their own, so if it had not been possible to transfer the genetic code for it, then efforts to transfer the Xa21 gene would have been ultimately fruitless. In addition, other research at the time discovered that another receptor code, named EFR and found in the model organism Arabidopsis, also confers the ability to fight against the bacterium, though not at as strong of a level. The upside is that the receptor seems to target the weaker strains that are less likely to set off a PRR response. Thus, if the two receptors are combined in a plant with the Xa21 gene, it is highly likely the resulting plant would exhibit a stronger and more rounded resistance response to bacterium infection from any of the subspecies varieties.[6]
With the varieties of rice and other disease resistant crops currently in field trial phases, it won’t be long before rice farmers around the world will be able to grow their crops without fear of them being taken out all at once by a bacterial infection. As a part of the overall regulatory testing for the soon to be for sale rice, an article to be published in the July edition of Food Chemistry looked at the nutritional composition and proteomics of the rice crop. It found, all in all, that there were no significant differences even genetically and epigenetically other than the changed gene and receptor, proving the specificity and accuracy of the techniques involved.[7]
Disease resistance research as a means to allow people to feed themselves is one of the most important fields of study in the world. Because with available food and good nutrition, populations are able to bring themselves out of subsistence farming and are able to focus on all the things that we call society. That which took us around the globe and into space, it all began because people were able to plant seeds and make food for themselves. It is a precious thing and, with all the diseases and pests out there, easily destroyed. Only with science and the efforts of people can we strive to protect it and to lift ourselves to the future.
References
- Economic Research Service. 2015 Feb 23. China continues to import rice at a record pace. United States Department of Agriculture; [accessed 2016 May 8]. http://www.ers.usda.gov/data-products/chart-gallery/detail.aspx?chartId=52010
- Sundaram RM, Chatterjee S, Oliva R, Laha GS, Cruz CV, Leach JE, Sonti RV. 2014. Update on Bacterial Blight of Rice: Fourth International Conference on Bacterial Blight.Rice [accessed 2016 May 8]; 7. http://thericejournal.springeropen.com/articles/10.1186/s12284-014-0012-7
- Tu J, Ona I, Zhang Q, Mew TW, Khush GS, Datta SK. 1998. Transgenic rice variety “IR72” with Xa21 is resistant to bacterial blight. Theoretical and Applied Genetics [accessed 2016 May 8]; 97:31–36. http://link.springer.com/article/10.1007/s001220050863
- Zhai W, Li X, Tian W, Zhou Y, Pan X, Cao S, Zhao X, Zhao B, Zhang Q, Zhu L. 2000. Introduction of a rice blight resistance gene,Xa21, into five Chinese rice varieties through an Agrobacterium-mediated system. Science in China Series C: Life Sciences [accessed 2016 May 8]; 43:361–368. http://link.springer.com/article/10.1007%2FBF02879300
- Tripathi JN, Lorenzen J, Bahar O, Ronald P, Tripathi L. 2014. Transgenic expression of the rice Xa21 pattern-recognition receptor in banana (Musa sp.) confers resistance to Xanthomonas campestris pv. Musacearum. Plant Biotechnology Journal [accessed 2016 May 8]; 12:663–673. http://www.ncbi.nlm.nih.gov/pubmed/24612254
- Schwessinger B, Bahar O, Thomas N, Holton N, Nekrasov V, Ruan D, Canlas PE, Daudi A, Petzold CJ, Singan VR, et al. 2015. Transgenic Expression of the Dicotyledonous Pattern Recognition Receptor EFR in Rice Leads to Ligand-Dependent Activation of Defense Responses. PLOS Pathogens [accessed 2016 May 8]; http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1004809
- Gayen D, Paul S, Sarkar SN, Datta SK, Datta K. 2016. Comparative nutritional compositions and proteomics analysis of transgenic Xa21 rice seeds compared to conventional rice. Food Chemistry [accessed 2016 May 8]; 15:301–307. http://www.ncbi.nlm.nih.gov/pubmed/26948618
Written by: Sterling Ericsson
Word Count: 866
Type: News Bite
