The National BioResource Project (NBRP) Lotus and Glycine in Japan

Mitochondrial succinate dehydrogenase function is essential for sperm motility and male fertility

Mitochondrial health is crucial to sperm quality and male fertility, but the precise role of mitochondria in sperm function remains unclear. SDHA is a component of the succinate dehydrogenase (SDH) complex and plays a critical role in mitochondria. In humans, SDH activity is positively correlated with sperm quality, and mutations in SDHA are associated with Leigh Syndrome. Here we report that the C. elegans SDHA orthologue SDHA-2 is essential for male fertility: sdha-2 mutants produce dramatically fewer offspring due to defective sperm activation and motility, have hyperfused sperm mitochondria, and disrupted redox balance. Similar sperm motility defects in sdha-1 and icl-1 mutant animals suggest an imbalance in metabolites may underlie the fertility defect. Our results demonstrate a role for SDHA-2 in sperm motility and male reproductive health and establish an animal model of SDH deficiency-associated infertility.

Distinct signaling routes mediate intercellular and intracellular rhizobial infection in Lotus japonicus

Rhizobial infection of legume roots during the development of nitrogen-fixing root nodules can occur intracellularly, through plant-derived infection threads traversing cells, or intercellularly, via bacterial entry between epidermal plant cells. Although it is estimated that around 25% of all legume genera are intercellularly infected, the pathways and mechanisms supporting this process have remained virtually unexplored due to a lack of genetically amenable legumes that exhibit this form of infection. In this study, we report that the model legume Lotus japonicus is infected intercellularly by the IRBG74 strain, recently proposed to belong to the Agrobacterium clade of the Rhizobiaceae. We demonstrate that the resources available for L. japonicus enable insight into the genetic requirements and fine-tuning of the pathway governing intercellular infection in this species. Inoculation of L. japonicus mutants shows that Ethylene-responsive factor required for nodulation 1 (Ern1) and Leu-rich Repeat Receptor-Like Kinase (RinRK1) are dispensable for intercellular infection in contrast to intracellular infection. Other symbiotic genes, including nod factor receptor 5 (NFR5), symbiosis receptor-like kinase (SymRK), Ca2+/calmodulin dependent kinase (CCaMK), exopolysaccharide receptor 3 (Epr3), Cyclops, nodule inception (Nin), nodulation signaling pathway 1 (Nsp1), nodulation signaling pathway 2 (Nsp2), cystathionine-β-synthase (Cbs), and Vapyrin are equally important for both entry modes. Comparative RNAseq analysis of roots inoculated with IRBG74 revealed a distinctive transcriptome response compared with intracellular colonization. In particular, several cytokinin-related genes were differentially regulated. Corroborating this observation, cyp735A and ipt4 cytokinin biosynthesis mutants were significantly affected in their nodulation with IRBG74, whereas lhk1 cytokinin receptor mutants formed no nodules. These results indicate a differential requirement for cytokinin signaling during intercellular rhizobial entry and highlight distinct modalities of inter- and intracellular infection mechanisms in L. japonicus.

Lotus japonicus Genetic, Mutant, and Germplasm Resources

A quarter of a century has passed since Lotus japonicus was proposed as a model legume because of its suitability for molecular genetic studies. Since then, a comprehensive set of genetic resources and tools has been developed, including recombinant inbred lines, a collection of wild accessions, published mutant lines, a large collection of mutant lines tagged with LORE1 insertions, cDNA clones with expressed sequence tag (EST) information, genomic clones with end-sequence information, and a reference genome sequence. Resource centers in Japan and Denmark ensure easy access to data and materials, and the resources have greatly facilitated L. japonicus research, thereby contributing to the molecular understanding of characteristic legume features such as endosymbiosis. Here, we provide detailed instructions for L. japonicus cultivation and describe how to order materials and access data using the resource center websites. The comprehensive overview presented here will make L. japonicus more easily accessible as a model system, especially for research groups new to L. japonicus research. © 2018 by John Wiley & Sons, Inc.

Naturally occurring diversity helps to reveal genes of adaptive importance in legumes

Environmental changes challenge plants and drive adaptation to new conditions, suggesting that natural biodiversity may be a source of adaptive alleles acting through phenotypic plasticity and/or micro-evolution. Crosses between accessions differing for a given trait have been the most common way to disentangle genetic and environmental components. Interestingly, such man-made crosses may combine alleles that never meet in nature. Another way to discover adaptive alleles, inspired by evolution, is to survey large ecotype collections and to use association genetics to identify loci of interest. Both of these two genetic approaches are based on the use of biodiversity and may eventually help us in identifying the genes that plants use to respond to challenges such as short-term stresses or those due to global climate change. In legumes, two wild species, Medicago truncatula and Lotus japonicus, plus the cultivated soybean (Glycine max) have been adopted as models for genomic studies. In this review, we will discuss the resources, limitations and future plans for a systematic use of biodiversity resources in model legumes to pinpoint genes of adaptive importance in legumes, and their application in breeding.

Robust in vitro assay system for quantitative analysis of parasitic root-knot nematode infestation using Lotus japonicus

Root-knot nematodes are sedentary endoparasites that induce permanent infestation sites inside the roots of a broad range of crop plants. The development of effective control strategies require understanding the root-knot nematode parasitic process, however, the key molecular determinants for host manipulation during infestation remain elusive. One limiting factor has been the lack of a standardized conventional method for quantitative measurement of host parasitism by root-knot nematodes, particularly one that enables efficient downstream analyses and is free from other biological sources of variability. We report here a robust, highly reproducible system for quantitative analysis of all stages of root-knot nematode infestation using the legume Lotus japonicus as the plant host. This system provides a high quality nematode inoculum that maintains consistency in juvenile age and viability even between independently prepared populations. An optimized root transformation protocol was also developed for L. japonicus to facilitate downstream molecular studies in conjunction with the quantitative assay. Hairy root transformation efficiencies up to 91% were achieved. Root-knot nematodes formed egg masses at the root surface of both intact plants and transgenic hairy root cultures within eight weeks, confirming the assay conditions support an efficient completion of the infestation cycle. The in vitro assay system described here is compatible with other plant hosts and will benefit agricultural biotechnology research as it now enables specific high-throughput screening of nematode resistance traits together with subsequent mechanistic elucidation of the causative factors.