Identification and Characterization of C-type Lectin Genes in Reniform Nematode
AdvisorJenkins, Johnie N.
Wubbenm Martin J.
CommitteePeterson, Daniel G.
Reniform nematode, Rotylenchulus reniformis is a semi-endoparasitic nematode infecting over 300 plant species including important fiber crops like cotton. Introgression of reniform nematode resistance from a distantly-related resistant species Gossypium longicalyx into cultivated upland species Gossypium hirsutum has been a challenge. An approach towards achieving nematode resistance in crop plants has been to identify candidate parasitism genes expressed in the nematode facilitating infection of host plant species, and silencing the same through reverse genetic approaches like RNAi. A cDNA library constructed from the sedentary female stage of reniform nematode revealed an EST coding for C-type lectins and occurring in high frequency. Identification and characterization of C-type lectins in reniform nematode is important in understanding the immune system of nematode and in planning strategies for the development of reniform nematode resistant cotton varieties. A total of 11 C-type lectin gene family members were identified across six life stages of reniform nematode, with each member expected to play a significant role in the development and parasitic establishment with the host plant. Conserved sites characteristic of C-type lectins found in other organisms have been identified in the C-type lectin genes in reniform nematode for binding of Ca+2 and mannose. The highest level of expression of C-type lectins was observed in the sedentary female stage indicating it to be possibly the most sensitive stage to microbial infection and so a likely stage to target for its management. The site of secretion of C-type lectins in the sedentary female stage could be identified by in situ hybridization as the hypodermal region of the exposed posterior body region which is not inserted into the host root tissue. Phylogenetic analyses of C-type lectin domains of various nematode groups placed the plant-parasitic nematodes in one group indicating the possibility of co-evolution and probably carrying out a similar function aiding in the establishment of parasitism with host plants. Our findings now extend the spectrum of known nematode C-type lectin genes and suggest that lectin activity might be a more general feature of parasitism which could be explored in better understanding the interactions occurring at the host-nematode and nematode-pathogen interfaces.