|Macdonald, Margaret - Peggy|
|Matthews, Benjamin - Ben|
Submitted to: Functional Plant Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/23/2014
Publication Date: 3/26/2014
Citation: Maldonado, A., Macdonald, M.H., Youssef, R.M., Brewer, E.P., Beard, H.S., Matthews, B.F. 2014. Modification of the expression of two NPR1 suppressors SNC1 and SNI1, in coybean (Glycine max) confers partial resistance to the soybean cyst nematode (Heterodera glycines). Functional Plant Biology. 41(7):714-726. Interpretive Summary: The soybean cyst nematode (SCN) is the most destructive pathogen of soybean in the US. Currently grown soybean varieties are not resistant to all field populations of SCN. We genetically engineered soybean roots to overexpress two Arabidopsis genes in soybean and to silence their counterparts. When we over expressed the Arabidopsis gene SNC1 in roots, the number of SCN cysts formed on the roots was reduced to 43% of control values. Overexpression of SNI1 had no significant effect. When we silenced the expression of the soybean SNC1 gene, there was no significant effect, but silencing of the soybean SNI1 gene reduced the number of SCN cysts formed to 60% of control values. Our results transfer knowledge gained from the model system, Arabidopsis, to soybean. Furthermore, they provide insights into the defense response of soybean to SCN, and they provide novel approaches for reducing SCN propagation.
Technical Abstract: Systemic acquired resistance (SAR) is an enhanced defense response triggered when plants detect a pathogen. The response is extended to uninfected organs to protect the plant from future pathogen attack. NPR1 is a nuclear leucine-rich repeat R protein with a key role in SAR. It binds specifically to salicylic acid, and it acts as a transcriptional coregulator of SAR activators and as an inhibitor of transcriptional repressors. The proteins encoded by SUPPRESSOR OF NPR1, CONSTITUTIVE (SNC1), and SUPPRESSOR OF NPR1, INDUCIBLE (SNI1), interact with NPR1 to regulate the expression of pathogenesis-related genes. The Arabidopsis snc1 mutant exhibits a constitutive resistance response, while in the sni1 mutant the SNI1 protein is rendered incapable of suppressing PR genes. To study the influence of SNC1 and SNI1 on resistance to the soybean cyst nematode, we transformed soybean roots separately with four constructs designed to: (i) overexpress GmSNC1, the soybean ortholog of AtSNC1, (ii) overexpress AtSNI1, (iii) silence GmSNC1, and (iv) silence GmSNI1, the soybean ortholog of AtSNI1. A significant reduction of the female nematode population was observed in treatments (i) and (iv). The expression of SAR marker genes was analyzed in these two treatments. The unusual pattern of expression of PR genes shows there are differences in the effect R genes have on soybean and Arabidopsis. Although NPR1 is involved in the cross-talk between the SA and JA/ET pathways, understanding of the nematode resistance mechanism in plants is still imprecise.