Macrophomina phaseolina expresses distinct waves of effectors and carbohydrate active enzymes during early (biotrophic), middle (necrotrophic), and late (saprotrophic) stages of infection

Authors: DILLA-ERMITA, JADE - University Of California; PENNERMAN, KAYLA - Oak Ridge Institute For Science And Education (ORISE); GUTIERREZ, OLIVIA - Former ARS Employee; Jimenez, Zoey; Ramos, Gerardo; INFANTE, SARA - Former ARS Employee; Goldman, Polly; Henry, Peter

Submitted to: Fungal Genetics Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/2/2024
Publication Date: 3/12/2024
Citation: Dilla-Ermita, J., Pennerman, K., Gutierrez, O., Jimenez, Z.D., Ramos, G., Infante, S., Goldman, P.H., Henry, P.M. 2024. Macrophomina phaseolina expresses distinct waves of effectors and carbohydrate active enzymes during early (biotrophic), middle (necrotrophic), and late (saprotrophic) stages of infection. Fungal Genetics Conference, March 12-17, 2024, Pacific Grove, California.

Interpretive Summary:

Technical Abstract: Macrophomina crown rot disease in strawberry, caused by Macrophomina phaseolina, has become more destructive in recent years as climate change-induced heat stress has exacerbated the disease. Several studies show that higher soil and air temperatures can increase disease severity by Macrophomina phaseolina, but the molecular mechanisms of this phenomenon are unknown. We hypothesized that higher temperatures accelerate the transition to necrotrophy, leading to upregulation of necrotrophy- and pathogenicity-related genes. To test our hypothesis, we conducted two growth chamber experiments with low (23'C day/18'C night) and high (30'C day/25'C night) temperature treatments. Plants were either inoculated by submersion in an 8% M. phaseolina mycelial suspension or sterile V8 broth. Disease severity was scored on a 1 to 5 scale and root tissues from five plants per treatment were harvested at 1-, 5-, 12-, and 21-days post inoculation (dpi) for RNA sequencing and microscopy. Root and crown necrosis, wilting, and plant death was accelerated and more severe in inoculated plants at high temperature compared to those at low temperature. A total of 2,330 differentially expressed genes were identified in the M. phaseolina transcriptome between different temperatures, timepoints, and disease scores. Analysis of weighted gene co-expression networks of 7,827 genes with transcriptomic evidence revealed 23 distinct gene modules. Gene modules with upregulated genes during early infection, late infection stages, and during saprotrophic growth on dead root tissues were observed. The early to mid-infection modules were enriched with genes encoding glycoside hydrolases, pectinesterases, and effectors. The profile of carbohydrate active enzyme (cazyme) and effector gene expression was distinct at later infection stages and the transition to these expression patterns occurred earlier for plants that were incubated at higher temperatures. Additionally, there were differentially expressed effectors and cazymes during plant death that resembled the gene expression of in vitro control. Our study demonstrated that the switch to necrotrophy occurred earlier at higher temperatures, as evidenced by the transition to necrotrophy-associated patterns of gene expression. More research is needed into whether the higher disease severity at increased temperatures is due to fungal growth rates or factors related to plant susceptibility.