Overexpression of MIC-3 indicates a direct role for the MIC gene family in mediating Upland cotton (Gossypium hirsutum) resistance to root-knot nematode (Meloidogyne incognita)

Authors: Wubben, Martin; Callahan, Franklin; Velten, Jeffrey; Burke, John; Jenkins, Johnie

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2014
Publication Date: 2/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60923
Citation: Wubben, M., Callahan, F.E., Velten, J.P., Burke, J.J., Jenkins, J.N. 2015. Overexpression of MIC-3 indicates a direct role for the MIC gene family in mediating Upland cotton (Gossypium hirsutum) resistance to root-knot nematode (Meloidogyne incognita). Theoretical and Applied Genetics. 128:199-209.

Interpretive Summary: Mounting circumstantial evidence has suggested that the cotton MIC-3 gene is involved in the resistance response of highly resistant cotton germplasm lines to root-knot nematode (RKN) infection. Both RKN-resistant and RKN-susceptible cotton lines possess the MIC-3 gene; however, MIC-3 is expressed earlier and at a much higher level after RKN infection in resistant versus susceptible plants. The purpose of this study was to determine whether overexpression of MIC-3 in a RKN-susceptible genetic background (i.e., Coker 312) would alter the plant’s susceptibility to RKN. In collaboration with ARS scientists in Lubbock, TX, transgenic cotton lines were developed that overexpressed MIC-3 at the mRNA and protein level in root tissues. We determined that MIC-3 overexpression reduced RKN reproduction by 60-75% in transgenic plants compared to non-transgenic Coker312. We also determined that the effect of MIC-3 overexpression was specific to RKN as no change in susceptibility to the reniform nematode was observed. These experiments strongly suggest that MIC-3 plays a vital role in mediating cotton resistance to RKN.

Technical Abstract: Major quantitative trait loci (QTL) have been mapped to Upland cotton (Gossypium hirsutum L.) chromosomes 11 and 14 that govern the highly resistant phenotype in response to infection by root-knot nematode (RKN; Meloidogyne incognita Chitwood & White); however, nearly nothing is known regarding the underlying molecular determinants of this RKN-resistant phenotype. Multiple lines of circumstantial evidence have strongly suggested that the MIC (Meloidogyne Induced Cotton) gene family plays an integral role in mediating cotton resistance to RKN. In this report, we demonstrate that overexpression of MIC-3 in a RKN-susceptible genetic background reduces RKN egg production by ca. 60-75% compared to non-transgenic controls and transgene-null sibling lines. MIC-3 transcript and protein overexpression was confirmed in root tissues of multiple independent transgenic lines with each line showing a similar level of increased resistance to RKN. In contrast to the effect on RKN fecundity, transgenic lines showed RKN-induced root galling similar to the susceptible controls. In addition, we determined that the effect of MIC-3 overexpression was specific to RKN as no effect was observed on reniform nematode (Rotylenchulus reniformis Linford & Oliveira) infection. Transgenic lines did not show obvious altered growth, morphology, flowering, or fiber quality traits. Gene expression analyses showed that MIC-3 transcript levels in uninfected transgenic roots exceeded levels observed in RKN-infected roots of naturally resistant plants and that overexpression did not alter the regulation of native MIC genes in the genome. These results are the first report describing a direct role for a specific gene family in mediating cotton resistance to a plant-parasitic nematode.