Comparative transcriptomic analysis of rubber (Hevea brasiliensis) clones differing in disease tolerance provides novel insights into the disease response associated with abnormal leaf fall disease caused by Phytophthora meadii

Abstract

Rubber is an important industrial commodity and Hevea brasiliensis is the commercial source of natural rubber (NR). Abnormal Leaf Fall (ALF) disease caused by Phytophthora meadii is one of the major diseases affecting yield of NR. Understanding Hevea-Phytophthora interaction mechanism is essential to manage this devastating disease. Transcriptome analysis was employed to gain an understanding on the molecular mechanisms that confer resistance to Phytophthora that would facilitate development of disease-tolerant Hevea clones. As our current understanding of Hevea-Phytophthora interaction is limited, an attempt was made to analyze and compare the transcriptomes of tolerant and susceptible clones of H. brasiliensis in response to P. meadii infection (in healthy and Phytophthora challenge-inoculated condition) during early, middle and late phases of infection by using the RNA-Seq technology. The transcriptome sequencing generated an average of 19,000 differentially expressed genes (DEGs) in both clones. When comparing the tolerant clone to the susceptible clone, there was an overall increase in the number of DEGs and a progression in the number of DEGs, indicating a more active engagement of transcriptional activity in the tolerant clone. Functional annotation, KEGG analysis and enrichment analysis revealed that the major pathways enriched for the DEGs were involved in plant hormone signal transduction and plant-pathogen interaction. An analysis of DEGs during each phase showed that the most active transcripts involved in defense mechanisms were activated during mid-phase and in the case of susceptible clone least transcripts were induced during mid-phase than in any other phase in both the clones. Many DEGs belonging to the MYB, NAC, WRKY and AP2/ERF transcription factor families were observed in both clones. Comparative studies revealed their differential involvement in tolerant and susceptible clones against Phytophthora infection. These findings may facilitate further exploration of Hevea-Phytophthora interaction and in cloning for defense related genes.