Identification of differentially expressed genes induced during the early events of sugarcane and Colletotrichum falcatum interaction

Abstract

To understand red rot resistance mechanisms, suppression subtractive hybridization (SSH) has been used in this study to identify the early events during sugarcane and C. falcatum interaction. A resistant variety Co 93009 and a highly susceptible variety CoC 671 were used for construction of SSH cDNA libraries. The resistant Co 93009 was used as tester and susceptible CoC 671 was used as driver. At the end of subtraction, cloning and sequencing the ESTs were classified into various functional categories based on homology search. A total of 317 annotatable ESTs were obtained from both the libraries, 146 corresponded to sugarcane response triggered at 12h after C. falcatum inoculation and 171 corresponded to sugarcane response triggered at 36h after C. falcatum inoculation. In both the libraries, several signal transduction genes were commonly expressed. Secondary metabolism plays a vital role in plant cells as a defense response which synthesizes secondary metabolites which are lethal for pathogens. S-adenosyl methionine (SAM) synthetase, involved in polyamine biosynthesis was expressed in 12h response library and dehydroquinate dehydratase involved in phenyl propanoid pathway was induced in the other library. Dirigent protein which is widely known for conifer defense and which is involved in dictating stereochemistry of lignin biosynthesis was found to be expressed in both the libraries but the transcript level was 15 in 36 h response libraries. The expression of a dirigent protein in response to C. falcatum challenge in sugarcane is a novel outcome which interlinks the architecture and molecular evolution of sugarcane and conifers. Apart from these, many transcripts involved in general metabolism, energy metabolism, transport and several transcription factors were expressed in both the libraries. In conclusion, this study identified key transcripts, several of which are not reported in sugarcane resistance response. Functional validation and gene silencing studies of key enzymes/transcripts makes them a suitable candidate for transgenic approaches or breeding programmes. Our studies are in progress to functionally validate candidate transcripts through qRT-PCR and to standardize gene silencing strategies