Abstract
The regulation of innate immunity and plant growth, along with the trade-off between them, affects the defense and recovery mechanisms of the plant after it is attacked by pathogens. Although it is known that hormonal crosstalk plays a major role in regulating interaction of plant growth and PAMP-triggered immunity, the relationship between plant growth and effector-triggered immunity (ETI) remains unclear. In a large-scale yeast two-hybrid screening for Pik-H4-interacting proteins, a homeodomain transcription factor OsBIHD1 was identified, which is previously known to function in biotic and abiotic stress responses. The knockout of OsBIHD1 in rice lines carrying Pik-H4 largely compromised the resistance of the rice lines to Magnaporthe oryzae, the fungus that causes rice blast. While overexpression of OsBIHD1 resulted in enhanced expression of the pathogenesis-related (PR) and ethylene (ET) synthesis genes. Moreover, OsBIHD1 was also found to directly bind to the promoter region of ethylene-synthesis enzyme OsACO3. In addition, OsBIHD1 overexpression or deficiency provoked dwarfism and reduced brassinosteroid (BR) insensitivity through repressing the expression of several critical genes involved in BR biosynthesis and BR signaling. During M. oryzae infection, transcript levels of the crucial BR catabolic genes (CYP734A2, CYP734A4, and CYP734A6) were significantly up-regulated in OsBIHD1-OX plants. Furthermore, OsBIHD1 was found to be capable of binding to the sequence-specific cis-elements on the promoters of CYP734A2 to suppress the plant growth under fungal invasion. Our results collectively suggest a model that OsBIHD1 is required for Pik-H4-mediated blast resistance through modulating the trade-off between resistance and growth by coordinating brassinosteroid-ethylene pathway.
Highlights
Plant growth and disease resistance have been regarded as two distinct and divergent systems
To confirm the specificity of this interaction, we sought to identify the OsBIHD1-interacting sites in the Pik1-H4 molecule which consists of four domains: coiled coil domain (CC), NBS, LRR (Leucine-rich repeats: 635–1040 aa), non-LRR domain
We showed in this study that the NBS-LRR protein Pik-H4 interacts with OsBIHD1 and the blast resistance by Pik-H4 depends on OsBIHD1
Summary
Plant growth and disease resistance have been regarded as two distinct and divergent systems. To fend off pathogens, plants must effectively integrate multiple signals including biotic and abiotic stressors to protect themselves from pathogen invasion (Wang and Wang, 2014). Plant defense responses such as pathogen-associated molecular pattern (PAMP)-triggered immunity. The Avr-PikD and Pikp-1 interaction has been recently dissected from the crystal structure (Lu et al, 2010) These studies illustrate the detailed molecular mechanism of an initial recognition event mediated by NLR proteins that integrate an immunity response to rice blast resistance. The panicle blast resistance protein Pb1 interacts with WRKY45 to regulate the SA immunity pathway. WRKY45 is an essential downstream regulator involved in Pb1-dependent blast resistance (Inoue et al, 2013)
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