Tian L, Shi S, Nasir F, Chang C, Li W, Tran LP, Tian C.

Rice (N Y). 2018 Apr 20;11(1):26. doi: 10.1186/s12284-018-0211-8.

Abstract

BACKGROUND:

Magnaporthe oryzae, the causal fungus of rice blast disease, negatively impacts global rice production. Wild rice (Oryza rufipogon), a relative of cultivated rice (O. sativa), possesses unique attributes that enable it to resist pathogen invasion. Although wild rice represents a major resource for disease resistance, relative to current cultivated rice varieties, no prior studies have compared the immune and transcriptional responses in the roots of wild and cultivated rice to M. oryzae.

RESULTS:

In this study, we showed that M. oryzae could act as a typical root-infecting pathogen in rice, in addition to its common infection of leaves, and wild rice roots were more resistant to M. oryzae than cultivated rice roots. Next, we compared the differential responses of wild and cultivated rice roots to M. oryzae using RNA-sequencing (RNA-seq) to unravel the molecular mechanisms underlying the enhanced resistance of the wild rice roots. Results indicated that both common and genotype-specific mechanisms exist in both wild and cultivated rice that are associated with resistance to M. oryzae. In wild rice, resistance mechanisms were associated with lipid metabolism, WRKY transcription factors, chitinase activities, jasmonic acid, ethylene, lignin, and phenylpropanoid and diterpenoid metabolism; while the pathogen responses in cultivated rice were mainly associated with phenylpropanoid, flavone and wax metabolism. Although modulations in primary metabolism and phenylpropanoid synthesis were common to both cultivated and wild rice, the modulation of secondary metabolism related to phenylpropanoid synthesis was associated with lignin synthesis in wild rice and flavone synthesis in cultivated rice. Interestingly, while the expression of fatty acid and starch metabolism-related genes was altered in both wild and cultivated rice in response to the pathogen, changes in lipid acid synthesis and lipid acid degradation were dominant in cultivated and wild rice, respectively.

CONCLUSIONS:

The response mechanisms to M. oryzae were more complex in wild rice than what was observed in cultivated rice. Therefore, this study may have practical implications for controlling M. oryzae in rice plantings and will provide useful information for incorporating and assessing disease resistance to M. oryzae in rice breeding programs.

See: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5910329/

Figure 1: Phenotype of non-inoculated and inoculated roots of cultivated and wild rice varieties. a Visible phenotype of roots of C, C + F, W and W + F groups. b, c, d and e Microscopic observation of safranin-stained roots of C (b), C + F (c), W (d) and W + F (e), respectively. The four treatments were non-inoculated cultivated rice (C), cultivated rice inoculated with Magnaporthe oryzae (C + F), non-inoculated wild rice (W), and wild rice inoculated with M. oryzae (W + F). Black lines are the scale bars, which represent 2 cm in (a) and 5 μm in (b, c, d, and e). Pink arrows indicate the representative parts of infected roots. Blue arrows indicate the plant epidermal regions, and orange arrows indicate the cortex regions