Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/28/2008
Publication Date: 6/1/2008
Citation: Wubben, M., Callahan, F.E., Hayes, R.W., Jenkins, J.N. 2008. Molecular characterization and temporal expression analyses indicate that the MIC (Meloidogyne Induced Cotton) gene family represents a novel group of root-specific defense-related genes in upland cotton (Gossypium hirsutum L.). Planta. 228:111-123. Interpretive Summary: The molecular genetic basis for root-knot nematode (RKN) resistance in Upland cotton is poorly understood. MIC3 (Meloidogyne Induced Cotton3) is a gene expressed within gall tissue of RKN-resistant plants but not in RKN-susceptible plants. In this paper, we identified fourteen genes highly similar to MIC3. In addition, we determined MIC3 expression in RKN-resistant roots was greatest immediately before resistance was physically visible in the resistant germplasm line ‘M315 RNR’ compared to the susceptible germplasm line ‘M8’. Many cotton genes have been identified that are expressed in response to infection by fungal or bacterial pathogens. These known defense-related genes showed similar levels of expression between RKN-resistant and susceptible plants following RKN infection. Increased MIC3 expression was not observed in M315 RNR or M8 following infection by the reniform nematode, to which M315 RNR is not resistant, nor in response to mechanical wounding of roots. Finally, MIC3 expression was undetectable in resistant cotton leaves infected with the bacterial blight pathogen. These results indicate MIC3 is part of a large gene family in Upland cotton specifically expressed in root tissues and may represent a group of novel defense-related genes. Furthermore, these results suggest that cotton resistance to RKN involves the expression of novel undiscovered defense genes.
Technical Abstract: The molecular events underlying the resistance of Upland cotton to the root-knot nematode (RKN) are largely unknown. In this report, we further characterize the previously identified MIC3 gene including the identification of fourteen related MIC cDNAs in nematode-infected roots of allotetraploid cotton. A time-course analysis of RKN infection in resistant and susceptible cotton lines showed that maximum MIC transcript accumulation occurred immediately prior to the phenotypic manifestation of resistance. MIC expression was non-inducible by wounding nor by reniform nematode infection during a compatible interaction. MIC expression was undetectable in cotton leaves undergoing a hypersensitive response to Xanthomonas campestris. An analysis of known defense gene expression (PR10, ERF5, CDNS, LOX1, POD4, POD8) in resistant and susceptible cotton roots showed that RKN infection specifically elicits the induction of MIC in resistant roots and not other common defense signaling pathways. These results indicate that cotton resistance to RKN involves novel defense signaling pathways and further supports the idea that the MIC genes are intimately involved in this resistance response and represent a group of root-specific defense-related genes in cotton.