A new study published in the Proceedings of the National Academy of Sciences
(PNAS) identifies a dominantly inherited mutation that confers resistance to
engineered cotton in caterpillars of the cotton bollworm, one of the world's
most destructive crop pests.

Entomologists from the University of Arizona (UA), the University of
Tennessee and the Nanjing Agricultural University in China collaborated in
this three-part study. Their goals were to identify the mutation conferring
Bt resistance in bollworms, precisely edit one bollworm gene to prove this
mutation causes resistance, and discover how the resistance is spreading
through cotton fields in China, where dominant bollworm resistance to Bt is
on the rise.

The researchers compared the DNA of resistant and susceptible bollworms, and
narrowed the search from 17,000 genes to a region of just 21 genes
associated with resistance. They found that 17 of those genes code for
proteins that are produced by the caterpillars. Bruce Tabashnik, Regents'
Professor in the UA College of Agriculture and Life Sciences' Department of
Entomology said that there was only one consistent difference in the 17
genes. There is one position where all of the resistant bollworms had one
DNA base pair and all of the susceptible bollworms had a different DNA base
pair. This pivotal base pair is in a newly identified gene named HaTSPAN1,
which codes for a tetraspanin - a protein containing four segments that span
cell membranes.



To determine if this single mutation causes resistance, the researchers used
the gene editing tool CRISPR to precisely alter only the HaTSPAN1 gene. When
the gene was disrupted in resistant bollworms, they became completely
susceptible to Bt. Conversely, when the mutation was inserted in the DNA of
susceptible bollworms, they became resistant - proving this single base pair
change alone causes resistance.



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