A parasitic plant Striga hermonthica has been causing huge damages to crop productions in African countries. A feasible method to prevent Striga infestation is to manipulate the host-parasite interaction by small molecules. Plant hormone strigolactones have been attractive targets since their first discovery as host-derived germination stimulants for Striga, although how Striga seeds sense strigolactones have long been unknown. Recent discovery of strigolactone receptors in Striga unveiled unique mechanism of strigolactone perceptions, and raises a hope to develop herbicides through rational design of small molecules. Here I review recent state of strigolactone research in Striga.

Recent advances in DNA sequencing technologies have enhanced our understanding of the diversity of microbes associated with plants in the field. Nonetheless, we have not yet developed frameworks for predicting and managing plant microbiomes, partly due to the complexity of host-symbiont and symbiont-symbiont interactions in natural conditions. Here, I discuss how we can gain the “bird’s-eye” view of interaction networks involving hundreds or thousands of microbial species and then explore “core microbes”, which have great impacts on whole microbiome dynamics and host plant physiology.

2-Azahypoxanthine （AHX, 1） and imidazole-4-carboxamide （ICA, 2） were isolated from a fairy-ring forming fungus Lepista sordida.　AHX was converted into a metabolite, 2-aza-8-oxohypoxanthine （AOH, 3）, in plants.　Afterward, it turned out that these three compounds, fairy chemicals （FCs）, endogenously exist in plants and are biosynthesized via a new purine metabolic pathway.　FCs gave tolerance to various stresses to plants and regulated growth of all the plants tested.　Furthermore, some metabolites of FCs were found.　In addition, FCs increased the yields of rice, wheat and other crops in green-house and/or field experiments.

Cultivated rice （Oryza sativa） produces various diterpenoid phytoalexins for defense, including phytocassanes, momilactones and oryzalexins. Carbon skeletons of the diterpenoid phytoalexins are biosynthesized from geranylgeranyl diphosphate via ent-copalyl diphosphate or syn-copalyl diphosphate, and the phytoalexins are generated by chemical modification of each carbon skeleton.　We identified diterpene cyclase genes that are responsible for forming the carbon skeletons of the phytoalexins: OsCPS2, CPS4, KSL4, KSL7, KSL8 and KSL10.　Other biosynthetic genes involved in the modification of the carbon skeletons, including cytochrome P450 （CYP） genes, have been identified, suggesting the existence of biosynthetic gene clusters for phytocassanes and momilactones.　In this review, we introduce the rice diterpenoid phytoalexin biosynthetic genes identified so far, and propose their possible evolutionary history.

Steroidal glycoalkaloids （SGAs） are toxic specialized metabolites that are found in Solanaceae.　Potato （Solanum tuberosum） contains the SGAs α-solanine and α-chaconine, which are biosynthesized from cholesterol.　Several biosynthetic genes including SSR2 and two cytochrome P450 genes （CYP72A188 and CYP72A208） have been identified, and the transgenic potato plants silencing these biosynthetic genes showed SGA-reduced phenotypes.　Here we summarize our recent results and strategy towards metabolic engineering of potato accumulating pharmaceutically useful compounds by genome editing.　CYP88B1, which is involved in a later step of the SGA biosynthetic pathway with unknown catalytic function, is co-ordinately expressed with the SGA biosynthetic genes.　We applied CRISPR/Cas9 system to knockout potato CYP88B1.　The CYP88B1-knockout potatoes showed no accumulation of SGAs, and furthermore the corresponding amounts of steroidal saponins were accumulated in the knockout potatoes.

Plants have the ability to synthesize and emit a diversity of volatile organic compounds （VOCs） that may act as aroma and flavor molecules in response to insect herbivores, mechanical wounding, and attraction of pollinators.　Plants also have the capacity to accumulate the VOCs into plant itself.　Several plant species morphologically develop specialized glandular trichomes to store VOCs which are released in response to tissue damage for chemical defense such as inhibiting microbial growth or deterring herbivores.　Glycosylation is another machinery for safely storing VOCs into normal cells.　Tea plant （Camellia sinensis） stores VOCs with glycosylation in tea leaves, mainly conjugated to β-primeverosides, the most abundant form of aroma diglycosides in C. sinensis.　Here, we introduced two UDP-glycosyltransferases （UGTs） from C. sinensis, UGT85K11 （CsGT1） and UGT94P1 （CsGT2）, converting VOCs into β-primeverosides by sequential glucosylation and xylosylation, respectively.　This information can be used to preserve tea aroma better during the manufacturing process and to investigate the mechanism of plant chemical defenses.

Ethylene is one of the major plant hormones, which is also known as inhibitor of potato sprouting during storage.　Through the morphological analysis in tuber sprouts, we have investigated differences of cell shapes between in sprouts stored under ethylene and in sprouts stored under control condition, no-ethylene;in control sprouts, the cell shapes elongated vertically, longitudinal direction, whereas in ethylene-stored sprouts, those cell shapes expanded horizontally long, instead of elongating vertically.　These results suggest that ethylene suppresses longitudinal cell-elongation in potato sprouts during storage.　Among sugar metabolism related-enzymes, the gene expression of β-amylase increased in early stage of storage under ethylene, suggesting that this causes to increase of reducing sugars in potato tubers in the early stage of storage under ethylene.

A rhizotron comprising a Petri dish filled with rock wool overlaid by glass fiber filter paper supplemented with nutrient solution was used to evaluate post-attachment resistance of rice against Striga hermonthica （Del.） Benth. under controlled environments. Compatibility of the parasite to the host observed in the rhizotron experiments is, in general, consistent with that observed under outdoor conditions. The rhizotron method also enabled to evaluate varietal differences in several resistance mechanisms that block the parasite from penetrating and developing.　These results verify the usefulness of the method to predict susceptibility of a host plant to the parasite and study plant-plant interactions taking place in the rhizosphere.

Since the decoding of Arabidopsis genome, big data of plant genes have been accumulated in public data bank and the expression of these genes have been analyzed.　By revealing relationships between the genes, co-expressed genes can be detected and thus, knowledge on the functionality of the genes can be obtained.　To reveal such relationships, we have developed ConfeitoGUIplus that is a toolkit to detect relationships between elements based on network analysis.　Here, we summarize the way to use this toolkit and introduce several examples of Arabidopsis gene expression datasets by focusing Myb transcription factors.　ConfeitoGUIplus can be used not only for gene expression but also for other datasets such as the accumulation of metabolites.　Although the present version of ConfeitoGUIplus only accepts a two-dimensional matrix containing elements and variates, in the near future, a correlation matrix such as relationships in gene homology and in molecular structure of metabolites will be acceptable to the toolkit.

Plant-parasitic nematodes cause substantial damage to agricultural crops world-wide.　The selective movement of nematodes toward known and unknown chemical cues is referred to as chemotaxis.　In the soil, chemotaxis is a complex phenomenon where interplay among multiple attractants and repellents produce long-range and short-range spatiotemporal signals for the nematodes.　Understanding the factors involved with plant-parasitic nematode chemotaxis is a scientifically intriguing topic that could lead to advances in managing these pests.　Here chemotactic behavior of plant-parasitic nematode is reviewed.

Nitrous oxide (N₂O) is a potent greenhouse gas and the predominant ozone depleting substance. The soybean rhizosphere is a site of active nitrogen (N) transformations, including those involving N₂O. Processes that produce N₂O occur in the soybean rhizosphere during the transformation of organic N inside the nodules to mineral N and then N₂O is either emitted to the atmosphere or further reduced to N₂ by N₂O reductase (N₂OR), which is encoded by the nos gene of soybean bradyrhizobia. Mutants of Bradyrhizobium diazoefficiens USDA110 with higher N₂OR activity (Nos⁺⁺ strains) than wild strains were generated under N₂O respiration by a mutator strategy. Emission of N₂O from soybean ecosystems was mitigated at the field scale by inoculation of soybean with Nos⁺⁺ strains of B. diazoefficiens. Comparative analysis of the Nos⁺⁺ mutant genomes showed that mutation of nasS gene encoding the NO₃⁻ sensor (NasS) of the two-component NasST regulatory system, induces N₂OR activity. Further studies showed that NasS and NasT form a complex that dissociates in the presence of NO₃⁻. Once dissociated, the anti-terminator NasT is able to interact with the 5′-leader region of nosR mRNA to interfere with the formation of a terminator structure and facilitate read-through transcription to induce nos expression. This knowledge improves our understanding of N-cycle biology in the legume rhizosphere and presents better options for global mitigation of N₂O emission from soils.