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Ramachandran, S. R.

Publications and source records attributed to Ramachandran, S. R..

2 recordsLinked to original sources

Haplotype-phased, chromosome-level, annotated genome assembly of the soybean rust pathogen Phakopsora pachyrhizi

Phakopsora pachyrhizi, the causal agent of soybean rust, is among the most aggressive and economically impactful pathogens affecting soybean (Glycine max) production worldwide. As a dikaryotic rust fungus, P. pachyrhizi maintains its genetic information as two discrete haplotypes that are sequestered within separate nuclei for most of its life cycle as it reproduces asexually via the production of infectious urediniospores. Previous genomes of three P. pachyrhizi isolates collected in South America revealed a large genome with a high transposable element content, measuring up to 1.25 Gb and 93%, respectively. Although these efforts provided valuable foundational resources, the complexity of the genome resulted in highly fragmented assemblies. Here, we generated a highly contiguous, substantially improved, annotated genome resource from the P. pachyrhizi isolate LA04-1, collected during the initial outbreak of soybean rust in the continental United States in 2004. The assembly is haplotype-phased, with each haplotype assembled into 18 chromosomes totaling 572 Mb and 569 Mb in size. The isolate contains unique mating-type genes and does not share haplotype genomes with any available isolates with whole-genome sequencing datasets. This resource will be valuable to future investigations into the underlying mechanisms of virulence in this important plant pathogen.

genomics↗

Rapid mini-chromosome divergence among fungal isolates causing wheat blast outbreaks in Bangladesh and Zambia

Global wheat production is seriously threatened by the filamentous fungal pathogen, Magnaporthe oryzae, causing wheat blast disease. The pathogen was first identified in South America and recently spread across continents to Bangladesh (South Asia) and Zambia (South-central Africa). M. oryzae strains closely related with a South American field isolate B71 was found to have caused the wheat blast outbreaks in South Asia and Africa. Here, we studied the genetic relationship among isolates found on the three continents. Using an improved reference genome for B71 and whole genome sequences of isolates from Bangladesh, Zambia, and South America, we found strong evidence to support that the outbreaks in Bangladesh and Zambia were caused by the introductions of genetically separated isolates. Structural variation analysis using whole genome short-read sequencing data indicate all isolates closely related to B71 maintained at least one supernumerary mini-chromosome and, interestingly, some Zambian isolates contain more than one mini-chromosome. Long-read sequencing and de novo genome assemblies of two Zambian isolates show that both contain a mini-chromosome similar to the B71 mini-chromosome, although pervasive structural variation exists among them. Genome assemblies also provide evidence that one Zambian isolate carries an additional mini-chromosome that is highly divergent from the B71 mini-chromosome. Our findings show that while the core genomes of the multiple introductions are highly similar, the mini-chromosomes have undergone marked diversification. The maintenance of the mini-chromosome during the multiple introductions, and the rapid sequence and structural variation suggests the mini-chromosomes may serve important virulence or niche adaptation roles under diverse environmental conditions.

genomics↗