Sheath blight resistance in rice is negatively regulated by WRKY53 via SWEET2a activation.

Sheath blight (ShB) is one of the most common diseases in rice that significantly affects yield production. However, the underlying mechanisms of rice defense remain largely unknown. Our previous transcriptome analysis identified that infection with Rhizoctonia solani significantly induced the expression level of SWEET2a, a member of the SWEET sugar transporter. The sweet2a genome-editing mutants were less susceptible to ShB. Further yeast-one hybrid, ChIP, and transient assays demonstrated that WRKY53 binds to the SWEET2a promoter to activate its expression. WRKY53 is a key brassinosteroid (BR) signaling transcription factor. Similar to the BR receptor gene BRI1 and biosynthetic gene D2 mutants, the WRKY53 mutant and overexpressor were less and more susceptible to ShB compared to wild-type, respectively. Inoculation with R. solani induced expression of BRI1, D2, and WRKY53, but inhibited MPK6 (a BR-signaling regulator) activity. Also, MPK6 is known to phosphorylate WRKY53 to enhance its transcription activation activity. Transient assay results indicated that co-expression of MPK6 and WRKY53 enhanced WRKY53 trans-activation activity to SWEET2a. Furthermore, expression of WRKY53 SD (the active phosphorylated forms of WRKY53) but not WRKY53 SA (the inactive phosphorylated forms of WRKY53), enhanced WRKY53-mediated activation of SWEET2a compared to expression of WRKY53 alone. Taken together, our analyses showed that R. solani infection may activate BR signaling to induce SWEET2a expression via WRKY53 through negative regulation of ShB resistance in rice.

Cell-wall-degrading enzymes produced in vitro and in vivo by Rhizoctonia solani, the causative fungus of peanut sheath blight.

Rhizoctonia solani causes the disease peanut sheath blight, involving symptoms of maceration and necrosis of infected tissue, mainly caused by cell-wall-degrading enzymes (CWDEs). This study investigated the production of CWDEs including polygalacturonase (PG), polymethyl-galacturonase (PMG), cellulase (Cx) and ß-glucosidase by R. solani in vitro (in liquid culture) and in vivo (in peanut plants). Significant PG, PMG, Cx and ß-glucosidase activities were detected in infected tissues including stalk and leaves of Baisha and Silihong peanut cultivars. Extracts of healthy tissue showed little or no such activities. In shaken liquid cultures of R. solani in medium containing pectin or pectin plus carboxymethyl cellulose (CMC) as the carbon source(s), PG and PMG were notably active. Significant Cx activity was detected in cultures with CMC or pectin plus CMC as the carbon source(s). However, only a very low level of ß-glucosidase activity was observed in cultures with any of the tested carbon sources. An increase of pH was recorded in decayed peanut tissues and liquid culture filtrates; the filtrate pH and fungal growth positively correlated. The fungal growth and/or pH were important factors for the production of PG, PMG and Cx in culture with pectin plus CMC as the carbon source. A single active PG isozyme with isoelectric point around 9.2 was detected in culture filtrates and in infected peanut tissues by the method of isoelectric focusing electrophoresis. The crude enzymes extracted from liquid culture of R. solani induced decay of healthy peanut leaves.

Mesorhizobium spp. are the main microsymbionts of Caragana spp. grown in Liaoning Province of China.

Caragana species are woody legumes widely distributed in the arid regions of China. These plants form root nodules but their nodule bacteria have not been clearly classified. A total of 112 symbiotic bacterial isolates were obtained from four Caragana species grown in Liaoning Province and were characterized with ARDRA, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins, BOX-PCR and sequencing of the 16S rRNA gene. Most of them were classified as Mesorhizobium belonging to 11 putative species. Three isolates were identified as Rhizobium etli and Burkholderia spp. This study offers new information about the Caragana-rhizobia association and resource for selection of inoculants used in sustainable agriculture and for further studies on the Caragana rhizobia.