Recent Insights in Rice Blast Disease Resistance

Identification of Enolase 1 as a Potential Target for Magnaporthe oryzae: Integrated Proteomic and Molecular Dynamics Simulation

Rice blast is an essential factor affecting rice yield and quality, which is caused by Magnaporthe oryzae (M. oryzae). Isobavachalcone (IBC) is a botanical fungicide derived from the seed extract of the Leguminosae plant Psoralea corylifolia L. and has shown an excellent rice blast control effect in field applications. To explore the potential targets of rice blast control, the analysis of the differentially expressed proteins (DEPs) between the liquid culture medium of mycelium treated by 10 mg/L of IBC for 2 h and the control group indicated that Enolase 1 (ENO1) was the most significantly down-regulated DEP with a fold change value of 0.305. In vitro experiments showed that after treating liquid culture mycelium with 10 mg/L of IBC for 0.5, 1, 2, 4, and 8 h, the enzymatic activity of ENO1 in the IBC experimental groups was 0.97, 0.75, 0.52, 0.44, and 0.39 times as much as in the control groups, respectively. To further explore the molecular interaction and binding mode between IBC and ENO1, the three-dimensional structure of ENO1 was established based on homology modeling. Molecular docking and molecular dynamics simulation showed that IBC had a pi-pi stacking effect with the residue TYR_365, a hydrogen bond interaction with the residue ARG_393, and hydrophobic interactions with non-polar residues ALA_361, LYS_362, and VAL_371 of ENO1. These findings indicated that ENO1 is a potential target of M. oryzae, which would pave the way for screening novel effective fungicides targeting ENO1.

Multilocus sequence analysis and identification of mating-type idiomorphs distribution in Magnaporthe oryzae population of Karnataka state of India

AIMS

To investigate the genetic diversity, population structure, and mating-type distribution among the eco-distinct isolates of Magnaporthe oryzae from Karnataka, India.

METHODS AND RESULTS

A set of 38 isolates of M. oryzae associated with leaf blast disease of rice were collected from different rice ecosystems of Karnataka, India, and analyzed for their diversity at actin, β-tubulin, calmodulin, translation elongation factor 1-α (TEF-1-α), and internal transcribed spacer (ITS) genes/region. The isolates were grouped into two clusters based on the multilocus sequence diversity, the majority being in cluster-IA (n=37), and only one isolate formed cluster-IB. Population structure was analyzed using 123 SNP data to understand the genetic relationship. Based on K=2 and ancestry threshold of >70%, blast strains were classified into two subgroups (SG1 and SG2) whereas, based on K=4 and ancestry threshold of >70%, blast strains were classified into four subgroups (SG1, SG2, SG3, and SG4). We have identified 13 haplotype groups where haplotype-group-2 was predominant (n=20) in the population. The Tajima's and Fu's Fs neutrality tests exhibited many rare alleles. Further, the mating-type analysis was also performed using MAT1 gene-specific primers to find the potentiality of sexual reproduction in different ecosystems. The majority of the isolates (54.5%) had MAT1-2 idiomorph, whereas 45.5 per cent of the isolates possessed MAT1-1 idiomorph.

CONCLUSIONS

The present study found the genetically homogenous population of M. oryzae by multilocus sequence analysis. Both mating types, MAT1-1 and MAT1-2, were found within the M. oryzae population of Karnataka.

SIGNIFICANCE AND IMPACT OF STUDY

The study on the population structure and sexual mating behavior of M. oryzae is important in developing region-specific blast-resistant rice cultivars. This is the first report of MAT1 idiomorphs distribution in the M. oryzae population in any Southern state of India.

Morpho-molecular diversity and avirulence genes distribution among the diverse isolates of Magnaporthe oryzae from Southern India

AIMS

To investigate the diversity of eco-distinct isolates of Magnaporthe oryzae for their morphological, virulence and molecular diversity and relative distribution of five Avr genes.

METHODS AND RESULTS

Fifty-two M. oryzae isolates were collected from different rice ecosystems of southern India. A majority of them (n = 28) formed a circular colony on culture media. Based on the disease reaction on susceptible cultivar (cv. HR-12), all 52 isolates were classified in to highly virulent (n = 28), moderately virulent (n = 11) and less-virulent (13) types. Among the 52 isolates, 38 were selected for deducing internal transcribed spacer (ITS) sequence diversity. For deducing phylogeny, another set of 36 isolates from other parts of the world was included, which yielded two distinct phylogenetic clusters. We identified eight haplotype groups and 91 variable sites within the ITS sequences, and haplotype-group-2 (Hap_2) was predominant (n = 24). The Tajima's and Fu's Fs neutrality tests exhibited many rare alleles. Furthermore, PCR analysis for detecting the presence of five Avr genes in the different M. oryzae isolates using Avr gene-specific primers in PCR revealed that Avr-Piz-t, Avr-Pik, Avr-Pia and Avr-Pita were present in 73.68%, 73.68%, 63.16% and 47.37% of the isolates studied, respectively; whereas, Avr-Pii was identified only in 13.16% of the isolates.

CONCLUSIONS

Morpho-molecular and virulence studies revealed the significant diversity among eco-distinct isolates. PCR detection of Avr genes among the M. oryzae population revealed the presence of five Avr genes. Among them, Avr-Piz-t, Avr-Pik and Avr-Pia were more predominant.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study documented the morphological and genetic variability of eco-distinct M. oryzae isolates. This is the first study demonstrating the distribution of the Avr genes among the eco-distinct population of M. oryzae from southern India. The information generated will help plant breeders to select appropriate resistant gene/s combinations to develop blast disease-resistant rice cultivars.