Uncovering novel sources of anthracnose resistance in populations of genetically diverse sorghums [Sorghum bicolor (L.) Moench]
Anthracnose (Colletotrichum sublineolum P. Henn., in Kabat and Bubák) is the major disease of sorghum [Sorghum bicolor (L.) Moench] in the Southeastern United States and the Caribbean, where the acreage of sorghum has been expanding rapidly in the past decade. The causal pathogen of anthracnose is a hemibiotrophic fungus: after an initial invasion of live plant cells, the fungus kills the plant tissue and obtains its nutrients from the necrotic tissue. Anthracnose resistance is the most effective and sustainable solution to ensuring sorghum biomass yield and biomass quality. During the past few years, multiple research efforts have been directed to identify new sources of resistance in the Sorghum Association Panel (SAP) and tropical germplasm, and to delimit genomic regions associated with the observed anthracnose resistant response. Nevertheless, these resistance loci only explained a limited portion of the observed variation indicating the existence of other resistance loci. This research project was directed to uncover anthracnose resistance loci present in the SAP and to validate previously identified resistance loci via introgression into susceptible sweet sorghums. In addition, U.S. National Plant Germplasm System (NPGS) tropical sorghum germplasm was evaluated to identify new sources of anthracnose resistance. Two recombinant inbred line (RIL) populations derived from SC265 and SC1103, which belong to the sorghum nested association mapping (NAM) population, were evaluated for anthracnose resistance response at Puerto Rico, Florida, Georgia, and Texas for two consecutive years. The SC265 RIL population was segregating for anthracnose resistance response against pathotypes from all four locations. However, the SC1103 RIL population segregated for anthracnose resistance only in Puerto Rico, Texas, and Florida. Two high-density linkage maps of 17,227 and 33,413 single nucleotide polymorphisms (SNPs) were constructed for the SC265 and SC1103 RIL populations, respectively, using genomic resources developed previously for the NAM. A genome scan found that anthracnose resistant response in line SC265 is controlled by a major locus on chromosome 6. Anthracnose resistant response in line SC1103 is controlled by two major loci on chromosomes 8 and 9. The locus on chromosome 8 was associated with the variation observed in Texas, Puerto Rico, and Florida, while the locus in chromosome 9 was associated with variation observed in Florida. These results confirmed that the SAP contains multiple anthracnose resistance sources at low frequency that could not be detected in genome-wide association analysis. The molecular function of these two resistance loci was investigated. Sobic.05G172300 is annotated as encoding an F-box protein that overlaps with an ascorbic acid mannose pathway regulator 1 domain, while Sobic.05G182400 is annotated as a protein tyrosine kinase with leucine-rich repeats. A combination of qRT-PCR-based gene expression studies and a high-throughput gene expression study (RNA-seq) followed by a gene expression network analysis indicated that in resistant accessions, the expression of these two genes increases in response to infection within 1 day after inoculation with C. sublineolum. Sobic05G172300 appears to be involved in the regulation of the production of reactive oxygen species (ROS) as a defense mechanism by controlling the amount of ascorbic acid that is produced. Sobic05G182400 is hypothesized to be the ortholog of Arabidopsis BAK1, to be confirmed by complementation studies that are in progress. Our working hypothesis is that in resistant genotypes the receptor-like kinase encoded by this gene negatively regulates cell death induced by C. sublineolum, thus extending the time the plant has to defend itself against the invading pathogen.
- Research Organization:
- Univ. of Florida, Gainesville, FL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER). Biological Systems Science Division
- DOE Contract Number:
- SC0019097
- OSTI ID:
- 1901813
- Report Number(s):
- DOE-UF0019097
- Country of Publication:
- United States
- Language:
- English
Similar Records
Genomic dissection of anthracnose resistance response in sorghum [Sorghum bicolor (L.) Moench]
Genomic dissection of anthracnose resistance response in sorghum [Sorghum bicolor (L.) Moench]