Erik Visser successfully defended his Ph.D. after he presented a Prestige Seminar entitled “Transcriptomic model of resistance mechanisms  in the Pinus-Fusarium circinatum interaction” on 18 April. Erik completed his PhD under the supervision of Prof. Sanushka Naidoo and co-supervision of Prof. Jill Wegrzyn (University of Connecticut), Prof. Emma Steenkamp and Prof. Zander Myburg. The external examiners were Prof. Nathaniel Street from Umeå University and Prof. Sofia Valenzuela from the University of Concepción, and the internal examiner was Prof. Brenda Wingfield.

Fusarium circinatum threatens both natural and industrial pine forests world-wide, affecting up to 60 pine species. A dual RNA-seq approach was used to compare host-pathogen interactions, at three and seven days post-inoculation (dpi), between F. circinatum resistant and susceptible pines, Pinus tecunumanii (low elevation) and P. patula respectively, during pathogen challenge. For each species, multiple de novo and genome-guided Trinity transcriptome assemblies were combined. Unigenes were annotated and filtered to remove non-pine sequences, resulting in 28,621 P. tecunumanii unigenes and 52,735 P. patula unigenes.

Host and pathogen differentially expressed genes (DEGs) were identified by mapping read data to a combined reference, consisting of the transcriptomes for F. circinatum and the respective host. Investigation of host expression over time in P. tecunumanii suggested important roles for ethylene and auxin signaling in early defence and salicylic acid and jasmonic acid signaling as well as ethylene and auxin signaling in late defence. In P. patula, host expression suggested delayed and compromised responses. The F. circinatum DEGs showed lower expression of key ergosterol biosynthesis genes in P. tecunumanii relative to P. patula, suggesting active suppression of pathogen growth in the resistant host.