Nutrient regulation of lipochitooligosaccharide recognition in plants via NSP1 and NSP2.

Many plants associate with arbuscular mycorrhizal fungi for nutrient acquisition, while legumes also associate with nitrogen-fixing rhizobial bacteria. Both associations rely on symbiosis signaling and here we show that cereals can perceive lipochitooligosaccharides (LCOs) for activation of symbiosis signaling, surprisingly including Nod factors produced by nitrogen-fixing bacteria. However, legumes show stringent perception of specifically decorated LCOs, that is absent in cereals. LCO perception in plants is activated by nutrient starvation, through transcriptional regulation of Nodulation Signaling Pathway (NSP)1 and NSP2. These transcription factors induce expression of an LCO receptor and act through the control of strigolactone biosynthesis and the karrikin-like receptor DWARF14-LIKE. We conclude that LCO production and perception is coordinately regulated by nutrient starvation to promote engagement with mycorrhizal fungi. Our work has implications for the use of both mycorrhizal and rhizobial associations for sustainable productivity in cereals.

The genetic architecture of host response reveals the importance of arbuscular mycorrhizae to maize cultivation.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in cultivated soils, forming symbiotic relationships with the roots of major crop species. Studies in controlled conditions have demonstrated the potential of AMF to enhance the growth of host plants. However, it is difficult to estimate the actual benefit in the field, not least because of the lack of suitable AMF-free controls. Here we implement a novel strategy using the selective incorporation of AMF-resistance into a genetic mapping population to evaluate maize response to AMF. We found AMF to account for about one-third of the grain production in a medium input field, as well as to affect the relative performance of different plant genotypes. Characterization of the genetic architecture of the host response indicated a trade-off between mycorrhizal dependence and benefit. We identified several QTL linked to host benefit, supporting the feasibility of breeding crops to maximize profit from symbiosis with AMF.

Population Connectivity in the Common Reef Zoantharian Zoanthus sansibaricus (Anthozoa: Hexacorallia) in Southern Japan.

Tropical and subtropical shallow benthic marine communities are highly diverse and balanced systems that constitute an important natural resource. Knowledge of the genetic diversity, connectivity and reproduction mode of each population is critical to understanding the fate of whole assemblages in times of disturbances. Importantly, the capability of populations to adapt to environmental challenges will be crucial to determining their survival. Here, we report on the population structure of the common reef zoantharian Zoanthus sansibaricus in the northwestern Pacific, by examining populations at three different locations in southern Japan using five highly variable microsatellite markers. Analyses of a population at the species' northern distribution limit combined with analyses of two subtropical populations suggest that habitat characteristics and ocean currents influence the connectivity and genetic diversity of this species. Our findings emphasize the adaptive ability of Z. sansibaricus to different environmental conditions and may help explain the wide distribution and generalist nature of this species.

Widely targeted metabolomics and coexpression analysis as tools to identify genes involved in the side-chain elongation steps of aliphatic glucosinolate biosynthesis.

Amino acid and glucosinolate biosynthesis are two interdependent pathways; amino acid synthesis as a part of primary metabolism provides the precursors for glucosinolate biosynthesis in secondary metabolism. In our previous studies, the combination of coexpression analysis and metabolite profiling led to the identification of genes and key regulators involved in glucosinolate biosynthesis. Moreover, the integration of transcriptome and metabolome data of sulphur-deprived Arabidopsis plants revealed coordinate changes in the expression profiles of genes involved in glucosinolate and amino acid metabolism.This review provides an overview of our recent studies involving Arabidopsis mutant plants that exhibit impairment in the side-chain elongation process occurring during aliphatic glucosinolate biosynthesis by means of coexpression analysis and a novel metabolite profiling approach based on ultra-performance liquid chromatography coupled with tandem quadrupole mass spectrometry (UPLC-TQMS) (Sawada et al. 2009a). Thus, this review highlights the advantages of the omics-based approach in identifying genes involved in glucosinolate biosynthesis.

Metabolomic screening applied to rice FOX Arabidopsis lines leads to the identification of a gene-changing nitrogen metabolism.

Plant metabolomics developed as a powerful tool to examine gene functions and to gain deeper insight into the physiology of the plant cell. In this study, we screened Arabidopsis lines overexpressing rice full-length (FL) cDNAs (rice FOX Arabidopsis lines) using a gas chromatography-time-of-flight mass spectrometry (GC-TOF/MS)-based technique to identify rice genes that caused metabolic changes. This screening system allows fast and reliable identification of candidate lines showing altered metabolite profiles. We performed metabolomic and transcriptomic analysis of a rice FOX Arabidopsis line that harbored the FL cDNA of the rice ortholog of the Lateral Organ Boundaries (LOB) Domain (LBD)/Asymmetric Leaves2-like (ASL) gene of Arabidopsis, At-LBD37/ASL39. The investigated rice FOX Arabidopsis line showed prominent changes in the levels of metabolites related to nitrogen metabolism. The transcriptomic data as well as the results from the metabolite analysis of the Arabidopsis At-LBD37/ASL39-overexpressor plants were consistent with these findings. Furthermore, the metabolomic and transcriptomic analysis of the Os-LBD37/ASL39-overexpressing rice plants indicated that Os-LBD37/ASL39 is associated with processes related to nitrogen metabolism in rice. Thus, the combination of a metabolomics-based screening method and a gain-of-function approach is useful for rapid characterization of novel genes in both Arabidopsis and rice.

Systematic approaches to using the FOX hunting system to identify useful rice genes.

Ectopic gene expression, or the gain-of-function approach, has the advantage that once the function of a gene is known the gene can be transferred to many different plants by transformation. We previously reported a method, called FOX hunting, that involves ectopic expression of Arabidopsis full-length cDNAs in Arabidopsis to systematically generate gain-of-function mutants. This technology is most beneficial for generating a heterologous gene resource for analysis of useful plant gene functions. As an initial model we generated more than 23,000 independent Arabidopsis transgenic lines that expressed rice fl-cDNAs (Rice FOX Arabidopsis lines). The short generation time and rapid and efficient transformation frequency of Arabidopsis enabled the functions of the rice genes to be analyzed rapidly. We screened rice FOX Arabidopsis lines for alterations in morphology, photosynthesis, element accumulation, pigment accumulation, hormone profiles, secondary metabolites, pathogen resistance, salt tolerance, UV signaling, high light tolerance, and heat stress tolerance. Some of the mutant phenotypes displayed by rice FOX Arabidopsis lines resulted from the expression of rice genes that had no homologs in Arabidopsis. This result demonstrated that rice fl-cDNAs could be used to introduce new gene functions in Arabidopsis. Furthermore, these findings showed that rice gene function could be analyzed by employing Arabidopsis as a heterologous host. This technology provides a framework for the analysis of plant gene function in a heterologous host and of plant improvement by using heterologous gene resources.