Pathogen-derived 9-methyl sphingoid base is perceived by a lectin receptor kinase in Arabidopsis

Kato, H., Nemoto, K., Shimizu, M., Abe, A., Asai, S., Ishihama, N., Daimon, T., Ojika, M., Kawakita, K., Onai, K., Shirasu, K., Ishiura, M., Takemoto, D., Takano, Y. and Terauchi, R. (2021). Pathogen-derived 9-methyl sphingoid base is perceived by a lectin receptor kinase in Arabidopsis. BioRxiv, 2021.10.18.464766. https://doi.org/10.1101/2021.10.18.464766

Abstruct

In plants, many invading microbial pathogens are recognized by cell-surface pattern recognition receptors (PRRs), inducing defense responses; yet how PRRs perceive pathogen sphingolipids remains unclear. Here, we show that the ceramide Pi-Cer D from a plant pathogenic oomycete Phytophthora infestans triggers defense responses in Arabidopsis. Pi-Cer D is cleaved by an Arabidopsis apoplastic ceramidase, NCER2, and the resulting 9-methyl-branched sphingoid base is recognized by a plasma membrane lectin receptor-like kinase, RDA2. Importantly, 9-methyl-branched sphingoid base, which is unique to microbes, induces plant immune responses by interacting with RDA2. Loss of RDA2 or NCER2 function compromised Arabidopsis resistance against an oomycete pathogen, indicating that these are crucial for defense. We provide new insights that help elucidate the recognition mechanisms of pathogen-derived lipid molecules in plants.

Fig. 4. A model for the recognition of pathogen-derived ceramide in plants. Pi-Cer D is cleaved by plant apoplastic ceramidase NCER2 into 9-methyl sphingoid base. 9-methyl sphingoid base is recognized by a lectin-receptor kinase, RDA2/SphingR, which then induces defense responses that include WRKY33 gene expression and enhances immunity against pathogen infection.

Population Genomics of Yams: Evolution and Domestication of Dioscorea Species

Sugihara, Y., Kudoh, A., Oli, M. T., Takagi, H., Natsume, S., Shimizu, M., Abe, A., Asiedu, R., Asfaw, A., Adebola, R. & Terauchi, R. (2021). Population Genomics of Yams: Evolution and Domestication of Dioscorea Species. In: Population Genomics. Springer, Cham. https://doi.org/10.1007/13836_2021_94

Abstruct

Yam is a collective name of tuber crops belonging to the genus Dioscorea. Yam is important not only as a staple food crop but also as an integral component of society and culture of the millions of people who depend on it. However, due to its regional importance, yam has long been regarded as an “orphan crop” lacking a due global attention. Although this perception is changing with recent advances in genomics technologies, domestication processes of most yam species are still ambiguous. This is mainly due to the complicated evolutionary history of Dioscorea species caused by frequent hybridization and polyploidization, which is possibly caused by dioecy that imposed obligate outcrossing to the species of Dioscorea. In this chapter, we provide an overview of the evolution of Dioscorea and address the domestication of yam from population genomics perspectives by focusing on the processes of hybridization and polyploidization. A review is given to the recent population genomics studies on the hybrid origin of D. rotundata in West and Central Africa, the global dispersion of D. alata through human migrations, and the whole-genome duplication of the South America species of D. trifida. In the end, we give a summary of current understanding of sex-determination system in Dioscorea.

RIL-StEp: epistasis analysis of recombinant inbred lines (RILs) reveals candidate interacting genes that control rice seed hull color and leaf chlorophyll content

Toshiyuki Sakai, Abe, A., Shimizu, M., Terauchi, R. (2021). RIL-StEp: epistasis analysis of rice recombinant inbred lines (RILs) reveals candidate interacting genes that control seed hull color and leaf chlorophyll contentG3 Genes|Genomes|Genetics, https://doi.org/10.1093/g3journal/jkab130

Abstract

Characterizing epistatic gene interactions is fundamental for understanding the genetic architecture of complex traits. However, due to the large number of potential gene combinations, detecting epistatic gene interactions is computationally demanding. A simple, easy-to-perform method for sensitive detection of epistasis is required. Due to their homozygous nature, use of recombinant inbred lines excludes the dominance effect of alleles and interactions involving heterozygous genotypes, thereby allowing detection of epistasis in a simple and interpretable model. Here, we present an approach called RIL-StEp (recombinant inbred lines stepwise epistasis detection) to detect epistasis using single-nucleotide polymorphisms in the genome. We applied the method to reveal epistasis affecting rice (Oryza sativa) seed hull color and leaf chlorophyll content and successfully identified pairs of genomic regions that presumably control these phenotypes. This method has the potential to improve our understanding of the genetic architecture of various traits of crops and other organisms.

Genome Analyses Reveal the Hybrid Origin of the Staple Crop White Guinea Yam (Dioscorea rotundata)

Yu Sugihara, Kwabena Darkwa, Hiroki Yaegashi, Satoshi Natsume, Motoki Shimizu, Akira Abe, Akiko Hirabuchi, Kazue Ito, Kaori Oikawa, Muluneh Tamiru-Oli, Atsushi Ohta, Ryo Matsumoto, Agre Paterne, David De Koeyer, Babil Pachakkil, Shinsuke Yamanaka, Satoru Muranaka, Hiroko Takagi, Ben White, Robert Asiedu, Hideki Innan, Asrat Asfaw, Patrick Adebola, Ryohei Terauchi (2020). Genome Analyses Reveal the Hybrid Origin of the Staple Crop White Guinea Yam (Dioscorea rotundata). PNAS, 117 (50) 31987-31992; DOI: 10.1073/pnas.2015830117.

Abstract

White Guinea yam (Dioscorea rotundata) is an important staple tuber crop in West Africa. However, its origin remains unclear. In this study, we resequenced 336 accessions of white Guinea yam and compared them with the sequences of wild Dioscorea species using an improved reference genome sequence of D. rotundata. In contrast to a previous study suggesting that D. rotundata originated from a subgroup of Dioscorea praehensilis, our results suggest a hybrid origin of white Guinea yam from crosses between the wild rainforest species D. praehensilis and the savannah-adapted species Dioscorea abyssinica. We identified a greater genomic contribution from D. abyssinica in the sex chromosome of Guinea yam and extensive introgression around the SWEETIE gene. Our findings point to a complex domestication scenario for Guinea yam and highlight the importance of wild species as gene donors for improving this crop through molecular breeding.

Lumi-Map, a real-time luciferase bioluminescence screen of mutants combined with MutMap, reveals Arabidopsis genes involved in PAMP-triggered immunity

Kato, H., Onai, K., Abe, A., Shimizu, M., Takagi, H., Tateda, C., Utsushi, H., Singkarabanit-Ogawa, S., Kitakura, S., Ono, E., Zipfel, C., Takano, Y., Ishiura, M., Terauchi, R. (2020). Lumi-Map, a real-time luciferase bioluminescence screen of mutants combined with MutMap, reveals Arabidopsis genes involved in PAMP-triggered immunity. Molecular Plant-Microbe Interactions, https://doi.org/10.1094/MPMI-05-20-0118-TA.

Abstract

Plants recognize pathogen-associated molecular patterns (PAMPs) to activate PAMP-triggered immunity (PTI). However, our knowledge of PTI signaling remains limited. In this report, we introduce Lumi-Map, a high-throughput platform for identifying causative single-nucleotide polymorphisms (SNPs) for studying PTI signaling components. In Lumi-Map, a transgenic reporter plant line is produced that contains a firefly luciferase (LUC) gene driven by a defense gene promoter, which generates luminescence upon PAMP treatment. The line is mutagenized and the mutants with altered luminescence patterns are screened by a high-throughput real-time bioluminescence monitoring system. Selected mutants are subjected to MutMap analysis, a whole-genome sequencing-based method of rapid mutation identification, to identify the causative SNP responsible for the luminescence pattern change. We generated nine transgenic Arabidopsis reporter lines expressing the LUC gene fused to multiple promoter sequences of defense-related genes. These lines generate luminescence upon activation of FLAGELLIN-SENSING 2 (FLS2) by flg22, a PAMP derived from bacterial flagellin. We selected the WRKY29-promoter reporter line to identify mutants in the signaling pathway downstream of FLS2. After screening 24,000 ethylmethanesulfonate-induced mutants of the reporter line, we isolated 22 mutants with altered WRKY29 expression upon flg22 treatment (abbreviated as awf mutants). Although five flg22-insensitive awf mutants harbored mutations in FLS2 itself, Lumi-Map revealed three genes not previously associated with PTI. Lumi-Map has the potential to identify novel PAMPs and their receptors as well as signaling components downstream of the receptors.