Two well-known plant virus proteins can block CRISPR-Cas13, a gene-editing system scientists are developing to give crops broad resistance to viruses, researchers at Kansas State University have found, Global Agriculture reported. The study, by a team under plant pathology professor David Cook, was published in the journal Stress Biology.
Unlike Cas9, which cuts DNA, Cas13 targets RNA. Many of the most damaging plant viruses, including potyviruses and tomato spotted wilt-type viruses, carry their genes as RNA, so a Cas13 system programmed with a guide matching a virus should destroy the virus's RNA as it copies itself, without permanently changing the plant's DNA.
The team worked in Nicotiana benthamiana, a tobacco relative used as a model plant, introducing the Cas13 enzyme LbuCas13 by agroinfiltration with guides against Turnip mosaic virus and against the plant's PDS gene, whose silencing turns leaves pale. Alongside it they expressed either HcPro, a potyvirus protein, or P19, a tombusvirus protein; both are suppressors that viruses use to disable the plant's own RNA defences. Both blocked Cas13 from silencing its targets.
A mutant of HcPro that has lost its suppressor activity failed to block Cas13, which indicates that the same activity viruses use to beat the plant's natural defence also defeats the engineered one. The authors suggest the suppressors may not tell Cas13's guide RNAs apart from the small RNAs of natural silencing and intercept both.
The practical message is a caution: a Cas13 trait that works against a weakened laboratory virus could fail against a field strain with a working suppressor. Future designs may need guide RNAs that resist suppressor binding, or a second resistance mechanism. Potyviruses damage potato, chilli and many vegetable and pulse crops, and Global Agriculture notes that the finding is relevant to seed and biotech companies in India and elsewhere working on gene-edited virus resistance.
Photo: Chandres / Wikimedia Commons (CC BY 3.0)
Source: Global Agriculture
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