Rice- Magnaporthe transcriptomics reveals host defense activation induced by red seaweed-biostimulant in rice plants

Abstract

Red seaweed extracts have been shown to trigger the biotic stress tolerance in several crops. However, reports on transcriptional modifications in plants treated with seaweed biostimulant are limited. To understand the specific response of rice to blast disease in seaweed-biostimulant-primed and non-primed plants, transcriptomics of a susceptible rice cultivar IR-64 was carried out at zero and 48 h post inoculation with Magnaporthe oryzae (strain MG-01). A total of 3498 differentially expressed genes (DEGs) were identified; 1116 DEGs were explicitly regulated in pathogen-inoculated treatments. Functional analysis showed that most DEGs were involved in metabolism, transport, signaling, and defense. In a glass house, artificial inoculation of MG-01 on seaweed-primed plants resulted in the restricted spread of the pathogen leading to the confined blast disease lesions, primarily attributed to reactive oxygen species (ROS) accumulation. The DEGs in the primed plants were defense-related transcription factors, kinases, pathogenesis-related genes, peroxidases, and growth-related genes. The beta-D-xylosidase, a putative gene that helps in secondary cell wall reinforcement, was downregulated in non-primed plants, whereas it upregulated in the primed plants indicating its role in the host defense. Additionally, Phenylalanine ammonia-lyase, pathogenesis-related Bet-v-I family protein, chalcone synthase, chitinases, WRKY, AP2/ERF, and MYB families were upregulated in seaweed and challenge inoculated rice plants. Thus, our study shows that priming rice plants with seaweed bio-stimulants resulted in the induction of the defense in rice against blast disease. This phenomenon is contributed to early protection through ROS, protein kinase, accumulation of secondary metabolites, and cell wall strengthening.

Keywords: Magnaporthe oryzae; biostimulants; blast disease; rice; seaweed; transcriptomics.

FIGURE 1

Challenge inoculation of MG-01 in primed and non-primed plants. Images of the rice leaves showing the impact of seaweed priming at different time intervals (A) Graphical representation of the lesion length in primed and non-primed plants at different intervals (B) where at 24 h, the LBD1 treated plants did not show any symptoms.

FIGURE 2

Induction of early defense through the production of ROS in primed plants at different time intervals. In vivo localization of superoxide radicals (A) and hydrogen peroxide (B) in response to MG-01 in primed and non-primed plants. Estimation of superoxide radicals (C) and hydrogen peroxide (D) at different intervals. Simple linear regression analysis (E) shows the correlation between superoxide radicals (SOR), hydrogen peroxide (H₂O₂), and lesion length.

FIGURE 3

Differentially expressed genes in primed and non-primed rice plants. Venn diagram showing the common and unique genes upregulated (A) and downregulated (B) in the comparative analyses. Heat maps showing the commonly up and downregulated genes in different treatments (C) and Defense-related genes up and downregulated in primed and non-primed plants (D).

FIGURE 4

qPCR validation of selected differentially expressed genes in different treatments. LOC_Os01g72530 (A), LOC_Os02g08440 (B), LOC_Os02g47470 (C), LOC_Os04g48290 (D), LOC_Os01g01660 (E), LOC_Os03g15370 (F), LOC_Os08g09060 (G), LOC_Os04g56430 (H), LOC_Os06g43304 (I), LOC_Os05g04500 (J), LOC_Os08g36760 (K), LOC_Os02g08440 (L), LOC_Os02g04130 (M), LOC_Os03g08330 (N), LOC_Os07g12340 (O), LOC_Os06g44010 (P), LOC_Os04g52090 (Q), LOC_Os08g36480 (R), LOC_Os05g24650 (S), and LOC_Os11g29720 (T).

FIGURE 5

Effect of seaweed biostimulant on leaf and neck blast disease in micro plot experiment. Representative images (A) of the leaf blast (Ai) and neck blast (Aii) in control and LBD1 sprayed plots. Percent disease index (PDI) (B) of leaf blast (Bi) and PDI of neck blast (ii) in different treatments. Grain yield in different treatments (Ci) and simple linear regression showing the correlation between yield, leaf, and neck blast (Cii).

FIGURE 6

Overview of the mechanism involved in defense against blast disease. A model represents the pathways activated to induce resistance against MG-01 in seaweed-primed rice plants. The recognition of elicitors and the receptors trigger the generation of NADPH molecules, subsequently leads to the production ROS after oxidation. This stimulus activates the kinase signaling molecules involed in signal transduction. These molecules activates the transcription factors (WRKY, MYB, and ZIP) which altogether results in the activation of the defence related genes.