FUNCTIONAL GENOMICS OF CEREAL DISEASE DEFENSE
Location: Corn Insects and Crop Genetics Research
Title: HvWRKY10, HvWRKY19, and HvWRKY28 positively regulate Mla-triggered immunity and basal defense to barley powdery mildew
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 12, 2012
Publication Date: July 30, 2012
Citation: Meng, Y., Wise, R.P. 2012. HvWRKY10, HvWRKY19, and HvWRKY28 positively regulate Mla-triggered immunity and basal defense to barley powdery mildew. Molecular Plant-Microbe Interactions. DOI:10.1094/MPMI-04-12-0082-R.
Interpretive Summary: Plant diseases are among the greatest deterrents to crop production worldwide. 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 WRKY transcription factors which are regulatory elements that control disease defense in plants.
By using an integrated functional genomics based approach, we have shown that barley WRKY10, WRKY19 and WRKY28 positively regulate resistance-gene mediated defense to powdery mildew, indicating that these WRKY proteins play key roles in effector-triggered immunity. However, comprehensive biochemical analyses did not reveal a direct interaction between these three nuclear-localized WRKY proteins and the disease resistance protein, MLA. This is significant, because it indicates that there are still unknown interacting factors that connect resistance proteins and their downstream effects on the plant phenotype.
These unique regulatory elements can control hundreds or thousands of other genes in the genome, which then influence 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 WRKY transcription factors as regulators of plant defense.
Impact: 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.
WRKY proteins represent a large family of transcription factors (TFs), involved in plant development and defense responses. So far, fifty-five unique barley TFs have been annotated that contain the WRKY domain; twenty-six of these are present on the Barley1 GeneChip. We analyzed time-course expression profiles of these 26 HvWRKY TFs in order to investigate their role in Mla (Mildew locus a)-mediated immunity to Blumeria graminis f. sp. hordei, the causal agent of powdery mildew disease. Comparisons of inoculation responsive Mla-specified interactions with B. graminis f. sp. hordei revealed that twelve HvWRKY TFs were differentially expressed; ten highly upregulated and 2 significantly downregulated. Barley stripe mosaic virus-induced gene silencing (BSMV-VIGS) of HvWRKY10, HvWRKY19 and HvWRKY28 compromised R-gene mediated defense to powdery mildew in genotypes harboring both Rar1-dependent and Rar1-independent Mla alleles, indicating that these WRKY TFs play key roles in effector-triggered immunity (ETI). Comprehensive Yeast-Two-Hybrid (Y2H) analyses, however, did not reveal a direct interaction between these three nuclear-localized WRKY TFs and MLA. Transient overexpression of all three WRKY TFs in lines carrying Mlo, which encodes a negative regulator of penetration resistance, significantly decreased susceptibility. Taken together, the above loss- and gain-of-function studies demonstrate that HvWRKY10, HvWRKY19 and HvWRKY28 act to positively regulate the barley transcriptome to respond to B. graminis f. sp. hordei invasion.