1.
Current understanding of pattern-triggered immunity and hormone-mediated defense in rice (Oryza sativa) in response to Magnaporthe oryzae infection.
Nasir, F, Tian, L, Chang, C, Li, X, Gao, Y, Tran, LP, Tian, C
Seminars in cell & developmental biology. 2018;:95-105
Abstract
Plant pathogens represent a huge threat to world food security, affecting both crop production and quality. Although significant progress has been made in improving plant immunity by expressing key, defense-related genes and proteins from different species in transgenic crops, a challenge remains for molecular breeders and biotechnologists to successfully engineer elite, transgenic crop varieties with improved resistance against critical plant pathogens. Upon pathogen attack, including infection of rice (Oryza sativa) by Magnaporthe oryzae, host plants initiate a complex defense response at molecular, biochemical and physiological levels. Plants perceive the presence of pathogens by detecting microbe-associated molecular patterns via pattern recognition receptors, and initiate a first line of innate immunity, the so-called pattern-triggered immunity (PTI). This results in a series of downstream defense responses, including the production of hormones, which collectively function to fend off pathogen attacks. A variety of studies have demonstrated that many genes are involved in the defense response of rice to M. oryzae. In this review, the current understanding of mechanisms that improve rice defense response to M. oryzae will be discussed, with special focus on PTI and the phytohormones ethylene, jasmonic acid, salicylic acid, and abscisic acid; as well as on the mediation of defense signaling mechanisms by PTI and these hormones. Potential target genes that may serve as promising candidates for improving rice immunity against M. oryzae will also be discussed.
2.
Transcriptome analysis reveals the molecular mechanisms of the defense response to gray leaf spot disease in maize.
Yu, Y, Shi, J, Li, X, Liu, J, Geng, Q, Shi, H, Ke, Y, Sun, Q
BMC genomics. 2018;(1):742
Abstract
BACKGROUND Gray leaf spot (GLS), which is caused by the necrotrophic fungi Cercospora zeae-maydis and Cercospora zeina, is one of the most impactful diseases in maize worldwide. The aim of the present study is to identify the resistance genes and understand the molecular mechanisms for GLS resistance. RESULTS Two cultivars, 'Yayu889' and 'Zhenghong532,' which are distinguished as resistant and susceptible cultivars, respectively, were challenged with the GLS disease and a RNA-seq experiment was conducted on infected plants at 81, 89, 91, and 93 days post planting (dap). Compared with the beginning stage at 81 dap, 4666, 1733, and 1166 differentially expressed genes (DEGs) were identified at 89, 91, and 93 dap, respectively, in 'Yayu889,' while relatively fewer, i.e., 4713, 881, and 722 DEGs, were identified in 'Zhenghong532.' Multiple pathways involved in the response of maize to GLS, including 'response to salicylic acid,' 'protein phosphorylation,' 'oxidation-reduction process,' and 'carotenoid biosynthetic process,' were enriched by combining differential expression analysis and Weighted Gene Co-expression Network Analysis (WGCNA). The expression of 12 candidate resistance proteins in these pathways were quantified by the multiple reaction monitoring (MRM) method. This approach identified two candidate resistance proteins, a calmodulin-like protein and a leucine-rich repeat receptor-like protein kinase with SNPs that were located in QTL regions for GLS resistance. Metabolic analysis showed that, compared with 'Zhenghong532,' the amount of salicylic acid (SA) and total carotenoids in 'Yayu889' increased, while peroxidase activity decreased during the early infection stages, suggesting that increased levels of SA, carotenoids, and reactive oxygen species (ROS) may enhance the defense response of 'Yayu889' to GLS. CONCLUSION By combining transcriptome and proteome analyses with comparisons of resistance QTL regions, calmodulin-like protein and leucine-rich repeat receptor-like protein kinase were identified as candidate GLS resistance proteins. Moreover, we found that the metabolic pathways for ROS, SA, and carotenoids are especially active in the resistant cultivar. These findings could lead to a better understanding of the GLS resistance mechanisms and facilitate the breeding of GLS-resistant maize cultivars.