Loose Plant Architecture 1-Interacting Kinesin-like Protein KLP Promotes Rice Resistance to Sheath Blight Disease

Fine mapping and candidate gene analysis of qSB12YSB, a gene conferring major quantitative resistance to rice sheath blight

KEY MESSAGE

qSB12YSB, a major quantitative sheath blight resistance gene originated from rice variety YSBR1 with good breeding potential, was mapped to a 289-Kb region on chromosome 12. Sheath blight (ShB), caused by Rhizoctonia solani kühn, is one of the most serious global rice diseases. Rice resistance to ShB is a typical of quantitative trait controlled by multiple quantitative trait loci (QTLs). Many QTLs for ShB resistance have been reported while only few of them were fine-mapped. In this study, we identified a QTL on chromosome 12, in which the qSB12YSB resistant allele shows significant ShB resistance, by using 150 BC4 backcross inbred lines employing the resistant rice variety YSBR1 as the donor and the susceptible variety Lemont (LE) as the recurrent parent. We further fine-mapped qSB12YSB to a 289-kb region by generating 34 chromosomal segment substitution lines and identified a total of 18 annotated genes as the most likely candidates for qSB12YSB after analyzing resequencing and transcriptomic data. KEGG analysis suggested that qSB12YSB might activate secondary metabolites biosynthesis and ROS scavenging system to improve ShB resistance. qSB12YSB conferred significantly stable resistance in three commercial rice cultivars (NJ9108, NJ5055 and NJ44) in field trials when introduced through marker assisted selection. Under severe ShB disease conditions, qSB12YSB significantly reduced yield losses by up to 13.5% in the LE background, indicating its great breeding potential. Our results will accelerate the isolation of qSB12YSB and its utilization in rice breeding programs against ShB.

Malectin Domain Protein Kinase (MDPK) Promotes Rice Resistance to Sheath Blight via IDD12, IDD13, and IDD14

Sheath blight (ShB) caused by Rhizoctonia solani is a major disease of rice, seriously affecting yield; however, the molecular defense mechanism against ShB remains unclear. A previous transcriptome analysis of rice identified that R. solani inoculation significantly induced MDPK. Genetic studies using MDPK RNAi and overexpressing plants identified that MDPK positively regulates ShB resistance. This MDPK protein was found localized in the endoplasmic reticulum (ER) and Golgi apparatus. Yeast one-hybrid assay, electrophoresis mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) showed that the intermediate domain proteins IDD12, IDD13, and IDD14 bind to the MDPK promoter. Moreover, IDD14 was found to interact with IDD12 and IDD13 to form a transcription complex to activate MDPK expression. The three IDDs demonstrated an additive effect on MDPK activation. Further genetic studies showed that the IDD13 and IDD14 single mutants were more susceptible to ShB but not IDD12, while IDD12, IDD13, and IDD14 overexpressing plants were less susceptible than the wild-type plants. The IDD12, IDD13, and IDD14 mutants also proved the additive effect of the three IDDs on MDPK expression, which regulates ShB resistance in rice. Notably, MDPK overexpression maintained normal yield levels in rice. Thus, our study proves that IDD12, IDD13, and IDD14 activate MDPK to enhance ShB resistance in rice. These results improve our knowledge of rice defense mechanisms and provide a valuable marker for resistance breeding.

Rhizoctonia solani Kühn Pathophysiology: Status and Prospects of Sheath Blight Disease Management in Rice

Sheath blight caused by necrotrophic fungus Rhizoctonia solani Kühn is one of the most serious diseases of rice. Use of high yielding semi dwarf cultivars with dense planting and high dose of nitrogenous fertilizers accentuates the incidence of sheath blight in rice. Its diverse host range and ability to remain dormant under unfavorable conditions make the pathogen more difficult to manage. As there are no sources of complete resistance, management through chemical control has been the most adopted method for sheath blight management. In this review, we provide an up-to-date comprehensive description of host-pathogen interactions, various control measures such as cultural, chemical, and biological as well as utilizing host plant resistance. The section on utilizing host plant resistance includes identification of resistant sources, mapping QTLs and their validation, identification of candidate gene(s) and their introgression through marker-assisted selection. Advances and prospects of sheath blight management through biotechnological approaches such as overexpression of genes and gene silencing for transgenic development against R. solani are also discussed.