|Xu, Weihui -|
|Meng, Yan -|
Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 8, 2013
Publication Date: March 1, 2014
Citation: Xu, W., Meng, Y., Wise, R.P. 2014. Mla- and Rom1-mediated control of microRNA398 and chloroplast copper/zinc superoxide dismutase regulates cell death in response to the barley powdery mildew fungus. New Phytologist. 201(4):1396-1412. Interpretive Summary: Plant diseases are among the greatest deterrents to crop production worldwide. Yet, although significant achievements have been made in investigating the mechanisms by which plant resistance (R) genes mediate disease defense, the signal transduction pathway triggered by these genes remains unclear. Powdery mildew is a devastating fungal disease, but also an ideal system to explore the interactions of fungal pathogens with their host plants. This manuscript describes novel and timely research on microRNA regulatory elements and their effect on resistance-gene mediated immunity. By using an integrated functional genomics based approach, we have shown that barley microRNA398 is regulated by the disease resistance protein, MLA, plus additional members of its interacting complex. This unique regulatory element controls the chloroplast copper/zinc superoxide dismutase protein, Hv-SOD1, which then influences barley cell death to halt progression of the disease. This discovery, also supported by the National Science Foundation-Plant Genome Research Program, establishes a previously unrecognized role for microRNAs as regulators of plant defense. Because common themes govern all plant-pathogen interactions, this finding provides new knowledge of broad significance to plant scientists, and to growers who utilize disease resistance to protect their crops.
Technical Abstract: Barley Mla (Mildew resistance locus a) confers allele-specific interactions with natural variants of the ascomycete fungus, Blumeria graminis f. sp. hordei (Bgh), causal agent of powdery mildew disease. Significant reprogramming of host gene expression occurs upon infection by this obligate biotrophic pathogen. To investigate whether changes in transcript accumulation manifest in the proteome, parallel samples from time-course Barley1 GeneChip profiles were analyzed using a proteomics-based approach. This revealed that loss-of-function mutations in Mla and Rar1 (Required for Mla resistance1) both result in the reduced accumulation of chloroplast copper/zinc superoxide dismutase Hv-SOD1. Further, microRNA profiling found that both Mla and Rom1 (Restoration of Mla resistance1) negatively regulate hvu-miR398, and that up-regulation of miR398 is correlated with reduced Hv-SOD1 expression. Heterologous over-expression of Arabidopsis miR398 represses translation of Hv-SOD1, and Barley stripe mosaic virus-induced gene silencing demonstrated that Hv-Sod1 plays an important role in Mla-triggered hypersensitive reaction (HR). Informatic analysis of the Hv-Sod1 promoter implicates multiple regulatory elements in plant disease resistance and stress. Taken together, these data indicate that Mla- and Rom1-regulated hvu-miR398 represses Hv-SOD1 translation, and that hvu-miR398-mediated feed-forward loops fine-tune Hv-Sod1 expression to influence barley HR in response to powdery mildew.