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Published on: August 4, 2018
Host Specificity Controlled by PWL1 and PWL2 Effector Genes in the Finger Millet Blast Pathogen Magnaporthe oryzae in
Hosea Isanda Masaki1, Santie de Villiers1,2, Peng Qi3,4
1Pwani University, Department of Biochemistry and Biotechnology, Kilifi, Kenya.
Abstract:
Magnaporthe oryzae, a devastating pathogen of finger millet (Eleusine coracana), secretes effector molecules during infection to manipulate host immunity. This study determined the presence of avirulence effector genes PWL1 and PWL2 in 221 Eleusine blast isolates from eastern Africa. Most Ethiopian isolates carried both PWL1 and PWL2. Kenyan and Ugandan isolates largely lacked both genes, and Tanzanian isolates carried either PWL1 or lacked both. The roles of PWL1 and PWL2 towards pathogenicity on alternative chloridoid hosts, including weeping lovegrass (Eragrostis curvula), were also investigated. PWL1 and PWL2 were cloned from Ethiopian isolate E22 and were transformed separately into Ugandan isolate U34, which lacked both genes. Resulting transformants harboring either gene gained varying degrees of avirulence on Eragrostis curvula but remained virulent on finger millet. Strains carrying one or both PWL1 and PWL2 infected the chloridoid species Sporobolus phyllotrichus and Eleusine tristachya, indicating the absence of cognate resistance (R) genes for PWL1 and PWL2 in these species. Other chloridoid grasses, however, were fully resistant, regardless of the presence of one or both PWL1 and PWL2, suggesting the presence of effective R genes against PWL and other effectors. Partial resistance in some Eragrostis curvula accessions to some blast isolates lacking PWL1 and PWL2 also indicated the presence of other interactions between fungal avirulence (AVR) genes and host resistance (R) genes. Related chloridoid species thus harbor resistance genes that could be useful to improve finger millet for blast resistance. Conversely, loss of AVR genes in the fungus could expand its host range, as demonstrated by the susceptibility of Eragrostis curvula to finger millet blast isolates that had lost PWL1 and PWL2. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
Insights
The study found that Magnaporthe oryzae avirulence genes PWL1 and PWL2 are present in Ethiopian finger millet blast isolates but largely absent in Kenyan and Ugandan ones. These genes confer avirulence on weeping lovegrass but not finger millet.
Area of Science:
- Plant Pathology
- Molecular Genetics
- Mycology
Background:
- Magnaporthe oryzae causes devastating finger millet blast, manipulating host immunity via secreted effector molecules.
- Avirulence genes, such as PWL1 and PWL2, play crucial roles in pathogen-host interactions and disease development.
Purpose of the Study:
- To determine the geographical distribution of PWL1 and PWL2 avirulence genes in eastern African Eleusine blast isolates.
- To investigate the role of PWL1 and PWL2 in pathogenicity on finger millet and alternative chloridoid hosts.
- To explore potential resistance genes in chloridoid species for improving finger millet blast resistance.
Main Methods:
- Screening of 221 Eleusine blast isolates from Ethiopia, Kenya, and Uganda for the presence of PWL1 and PWL2 genes.
- Cloning and transformation of PWL1 and PWL2 into a susceptible Ugandan isolate (U34) to assess pathogenicity.
- Evaluating the virulence of transformed isolates on finger millet (Eleusine coracana) and various chloridoid grass species.
Main Results:
- Most Ethiopian isolates harbored both PWL1 and PWL2, while Kenyan and Ugandan isolates largely lacked these genes.
- Transformants expressing PWL1 or PWL2 showed avirulence on Eragrostis curvula but remained virulent on finger millet.
- Chloridoid species Sporobolus phyllotrichus and Eleusine tristachya lacked resistance genes against PWL1 and PWL2, while others possessed effective resistance.
Conclusions:
- Geographical variation in PWL1 and PWL2 distribution suggests potential for host-specific adaptation in Magnaporthe oryzae.
- Chloridoid grasses harbor resistance genes that could be valuable for breeding blast-resistant finger millet varieties.
- Loss of avirulence genes in M. oryzae can lead to an expanded host range, highlighting the dynamic interplay between pathogen effectors and host immunity.
