Transcriptomic and metabolomic analyses identify a role for chlorophyll catabolism and phytoalexin during Medicago nonhost resistance against Asian soybean rust.
Asian soybean rust (ASR) caused by Phakopsora pachyrhizi is a devastating foliar disease affecting soybean production worldwide. Understanding nonhost resistance against ASR may provide an avenue to engineer soybean to confer durable resistance against ASR. We characterized a Medicago truncatula-ASR pathosystem to study molecular mechanisms of nonhost resistance. Although urediniospores formed appressoria and penetrated into epidermal cells of M. truncatula, P. pachyrhizi failed to sporulate. Transcriptomic analysis revealed the induction of phenylpropanoid, flavonoid and isoflavonoid metabolic pathway genes involved in the production of phytoalexin medicarpin in M. truncatula upon infection with P. pachyrhizi. Furthermore, genes involved in chlorophyll catabolism were induced during nonhost resistance. We further characterized one of the chlorophyll catabolism genes, Stay-green (SGR), and demonstrated that the M. truncatula sgr mutant and alfalfa SGR-RNAi lines showed hypersensitive-response-like enhanced cell death upon inoculation with P. pachyrhizi. Consistent with transcriptomic analysis, metabolomic analysis also revealed the accumulation of medicarpin and its intermediate metabolites. In vitro assay showed that medicarpin inhibited urediniospore germination and differentiation. In addition, several triterpenoid saponin glycosides accumulated in M. truncatula upon inoculation with P. pachyrhizi. In summary, using multi-omic approaches, we identified a correlation between phytoalexin production and M. truncatula defense responses against ASR.
1] Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA [2] Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
Yasuhiro
Y
Ishiga
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Srinivasa Rao
SR
Uppalapati
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Upinder S
US
Gill
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
David
D
Huhman
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Yuhong
Y
Tang
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA.
Kirankumar S
KS
Mysore
D002734:Chlorophyll / Q000378:metabolism*; D060467:Disease Resistance; D017343:Genes, Plant; D018525:Germination; D029902:Medicago / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology; D053858:Metabolic Networks and Pathways; D055442:Metabolome; D000067563:Phakopsora pachyrhizi / Q000502:physiology*; D036343:Pterocarpans / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012503:Saponins / Q000378:metabolism; D012717:Sesquiterpenes / Q000378:metabolism; D013172:Spores, Fungal / Q000502:physiology; D059467:Transcriptome; D014315:Triterpenes / Q000378:metabolism; D000094162:Phytoalexins
D036343:Pterocarpans; D017382:Reactive Oxygen Species; D012503:Saponins; D012717:Sesquiterpenes; D014315:Triterpenes; D002734:Chlorophyll; C047353:medicarpin; D000094162:Phytoalexins