Hongpo Wu

Setaria italica (foxtail millet), a founder crop of East Asian agriculture, is a model plant for C4 photosynthesis and developing approaches to adaptive breeding across multiple climates. Here we established the Setaria pan-genome by assembling 110 representative genomes from a worldwide collection. The pan-genome is composed of 73,528 gene families, of which 23.8%, 42.9%, 29.4% and 3.9% are core, soft core, dispensable and private genes, respectively; 202,884 nonredundant structural variants were also detected. The characterization of pan-genomic variants suggests their importance during foxtail millet domestication and improvement, as exemplified by the identification of the yield gene SiGW3, where a 366-bp presence/absence promoter variant accompanies gene expression variation. We developed a graph-based genome and performed large-scale genetic studies for 68 traits across 13 environments, identifying potential genes for millet improvement at different geographic sites. These can be used in marker-assisted breeding, genomic selection and genome editing to accelerate crop improvement under different climatic conditions.

It is generally accepted in plant-microbe interactions research that disease is the exception rather than a common outcome of pathogen attack. However, in nature, plants with symptoms that signify colonization by obligate biotrophic powdery mildew fungi are omnipresent. The pervasiveness of the disease and the fact that many economically important plants are prone to infection by powdery mildew fungi drives research on this interaction. The competence of powdery mildew fungi to establish and maintain true biotrophic relationships renders the interaction a paramount example of a pathogenic plant-microbe biotrophy. However, molecular details underlying the interaction are in many respects still a mystery. Since its introduction in 1990, the Arabidopsis-powdery mildew pathosystem has become a popular model to study molecular processes governing powdery mildew infection. Due to the many advantages that the host Arabidopsis offers in terms of molecular and genetic tools this pathosystem has great capacity to answer some of the questions of how biotrophic pathogens overcome plant defense and establish a persistent interaction that nourishes the invader while in parallel maintaining viability of the plant host.

Abstract The atmospheric pollutant ozone (O 3 ) is a strong oxidant that causes extracellular reactive oxygen species (ROS) formation, has significant ecological relevance, and is used here as a non‐invasive ROS inducer to study plant signalling. Previous genetic screens identified several mutants exhibiting enhanced O 3 sensitivity, but few with enhanced tolerance. We found that loss‐of‐function mutants in Arabidopsis MLO2 , a gene implicated in susceptibility to powdery mildew disease, exhibit enhanced dose‐dependent tolerance to O 3 and extracellular ROS, but a normal response to intracellular ROS. This phenotype is increased in a mlo2 mlo6 mlo12 triple mutant, reminiscent of the genetic redundancy of MLO genes in powdery mildew resistance. Stomatal assays revealed that enhanced O 3 tolerance in mlo2 mutants is not caused by altered stomatal conductance. We explored modulation of the mlo2 ‐associated O 3 tolerance, powdery mildew resistance, and early senescence phenotypes by genetic epistasis analysis, involving mutants with known effects on ROS sensitivity or antifungal defence. Mining of publicly accessible microarray data suggests that these MLO proteins regulate accumulation of abiotic stress response transcripts, and transcript accumulation of MLO2 itself is O 3 responsive. In summary, our data reveal MLO2 as a novel negative regulator in plant ROS responses, which links biotic and abiotic stress response pathways.

Powdery mildew, caused by Blumeria graminis f. sp tritici (Bgt) is one of the devastating diseases of wheat and causes yield losses in temperate wheat growing regions. A wheat line, N0308 with resistance to powdery mildew was used in this study. A suppression subtractive hybridization cDNA library was constructed from the wheat leaves inoculated by Bgt at the two-leaf stage. The differentially expressed genes in response to Bgt infection in wheat were identified, and a total of 175 positive clones from the library were sequenced, and 90 expressed sequence tags (ESTs) were subjected to clustering, BLAST alignment, functional annotation, and classification into different categories. By comparing the EST sequences among the SSH-cDNA libraries, we analyzed gene expression patterns of 7 ESTs associated with the resistance reaction of powdery mildew by using semi-quantitative reverse transcription-polymerase chain reaction. The expression of 5 genes (sulfatase, pathogenesis-related protein 17, betacarbonic anhydrase 2, thioredoxin h-like protein, and coronatine-insensitive) transcripts was induced, and the transcript levels of these genes were the highest at 72 h after Bgt infection, while those of 2 genes (violaxanthin de-epoxidase and gag-pol-polyprotein) were the highest level at 12 and 18 h post-infection, respectively. These findings suggest that these genes are induced at an early stage of infection and are transcriptionally activated for the host defense response.

Recessively inherited mutant alleles of Mlo genes (mlo) confer broad-spectrum penetration resistance to powdery mildew pathogens in angiosperm plants. Although a few components are known to be required for mlo resistance, the detailed molecular mechanism underlying this type of immunity remains elusive. In this study, we identified alloxan (5,5-dihydroxyl pyrimidine-2,4,6-trione) and some of its structural analogs as chemical suppressors of mlo-mediated resistance in monocotyledonous barley (Hordeum vulgare) and dicotyledonous Arabidopsis thaliana. Apart from mlo resistance, alloxan impairs nonhost resistance in Arabidopsis. Histological analysis revealed that the chemical reduces callose deposition and hydrogen peroxide accumulation at attempted fungal penetration sites. Fluorescence microscopy revealed that alloxan interferes with the motility of cellular organelles (peroxisomes, endosomes and the endoplasmic reticulum) and the pathogen-triggered redistribution of the PEN1/SYP121 t-SNARE protein. These cellular defects are likely the consequence of disassembly of actin filaments and microtubules upon alloxan treatment. Similar to the situation in animal cells, alloxan elicited the temporary accumulation of reactive oxygen species (ROS) in cotyledons and rosette leaves of Arabidopsis plants. Our results suggest that alloxan may destabilize cytoskeletal architecture via induction of an early transient ROS burst, further leading to the failure of molecular and cellular processes that are critical for plant immunity.