Arbuscular mycorrhizal （AM） fungi in the phylum Glomeromycota form mutualistic, symbiotic associations with the roots of more than 80% of land plants. The fungi are obligate symbionts incapable of completing their life cycle in the absence of a host. The critical developmental step in their life cycle is hyphal branching, which helps them to ensure contact with the host root and the establishment of symbiosis. We isolated a branching factor from the root exudates of Lotus japonicus and identified it as a strigolactone （SL）, 5-deoxystrigol. SLs are a group of terpene lactones, previously isolated as seed-germination stimulants for the parasitic weeds Striga and Orobanche. SLs were later shown to act as endogenous hormones, or their biosynthetic precursors, that regulate shoot branching. We showed that the structural requirements of SLs for biological activity in AM fungi are similar but not identical to those observed in plants and root parasitic weeds. Carlactone （CL） was first identified as a product of three SL biosynthetic enzymes in vitro. We demonstrated that CL is an endogenous biosynthetic precursor for canonical SLs and that CL undergoes three step oxidation at C-19 by the cytosolic cytochrome P450 MAX1 to carlactonoic acid, which is further converted to methyl carlactonoate which had been tentatively identified as SL-LIKE 1 in Arabidopsis. We also found that not only canonical SLs, but also CL-type SLs can induce hyphal branching in AM fungi.

Targeted modification of plant genome is the key for elucidating and manipulating gene functions in basic research and breeding.　Recently, successful genome editing using engineered nucleases has been increasing rapidly in both model plants and crops.　Furthermore, improvement of engineered nuclease itself and development of delivery methods is progressing rapidly.　Thus, it is certain that genome editing will attract further public attention near future.　In this review, we describe an overview of recent advances in genome editing technologies in plants.　We hope this review promote understanding of present situation and provide new insights into plant biology and molecular breeding technology.

In the microbial type-II CRISPR-Cas （clustered regularly interspaced short palindromic repeat and CRISPR-associated）adaptive immune system, the RNA-guided DNA endonuclease Cas9 is responsible for the degradation of foreign genetic elements. Using dual RNA guides or a single chimeric RNA guide, Cas9 can recognize and cleave a double-stranded DNA target complementary to the RNA guide. Thus, Cas9 has been harnessed for numerous technologies, such as genome editing, epigenome editing and chromosome imaging. Recent structural studies provided mechanistic insights into the RNA-guided DNA recognition and cleavage by Cas9. The crystal structures revealed that Cas9 adopts a bilobed architecture, and recognizes the guide RNA-target DNA heteroduplex within the central channel between the two lobes in a non-sequence-specific manner, thereby explaining the RNA-guided DNA recognition by Cas9. In addition, the structures revealed that the HNH and RuvC endonuclease domains are located at positions suitable for cleaving the two strands in the unwound DNA target. Furthermore, the structural information facilitated the development of engineered Cas9 variants, such as those with enhanced cleavage fidelity or altered DNA-targeting specificities.

Current genome editing tools are based on the artificial programmable nucleases, which induce DNA double strand break which may cause formation of insertion and deletion at the target site.　For more precise modification, homologous templates are needed to be co-introduced to induce homology-mediated transformation at the cleaved site, although success rate for this is not always high enough, especially in planta.　In place of the nuclease-based, conventional genome editing technology, deaminase-mediated genome editing has been developed and applied to plants.　Target-AID and Base Editor, which employ cytidine deaminase PmCDA1 and rApobec respectively tethered to nuclease-deficient CRISPR-Cas9 system, can specifically deaminate cytidines to form uracil on DNA, which mainly causes C to T mutagenesis.　These systems were optimized for expression in plants and successfully demonstrated in rice, wheat, corn and tomato using agrobacterium-mediated transformation or particle bombardment.　Advanced technology such as DNA-free transformation will be addressed in the future studies.

Peptides are versatile tools in biotechnology, especially in gene/protein delivery area.　The individual character of each amino acid can be combined, resulting in huge advantage for targeted delivery systems.　The author’s group recently reported the efficient fusion peptide-based delivery of proteins into intact Arabidopsis thaliana.　General plant transformation methods can cause random integration of exogenous DNA into the plant genome.　To avoid these events, the direct introduction of protein into intact plants was reported.　This efficient protein delivery system would be a powerful tool in plant biotechnology and breeding.

Methods for stably transforming the mitochondrial genomes of multicellular organisms are presently unavailable.　Plant mitochondrial genomes encode genes not only for essential oxidative phosphorylation but also for agronomically important traits, such as cytoplasmic male sterility.　The lack of transformation methods prevents analysis of basic features of the genomes and their encoding genes, and prevents their application to agriculture.　Recently, a TALEN-based method was used to eliminate some mammalian mitochondrial disease genes.　Unlike mammalian mitochondrial genomes, plant mitochondrial genomes are large and vary in size.　They have many recombination-active repeats, and linear, branched and circular structures.　These complicated and dynamic structures make them difficult to stably transform, and this in turn makes it difficult to understand the molecular mechanisms underlying their complex structures.　This review describes the unusual features of plant mitochondrial genomes and recent attempts to transform the mitochondrial genomes of plants and other organisms.

Separated sexuality （dioecy） is one of the most important strategies to promote or maintain genetic diversity in a species, both in plants and animals.　Dioecious sex determining system has been established several times independently during evolution in seed plants, which would explain lineage-specific adaptive scenarios.　Yet, little has been known on genetic determinants of dioecy and their functional pathways, since the first discovery of a plant sex chromosome in 1917.　In 2014, as the first report of sex determinants in dioecious plants, a Y chromosome-encoded small-RNA, named OGI, and its counterpart located on an autosome, named MeGI, were identified in persimmons （Diospyros spp.）.　Furthermore, this dioecious system has evolved to give more flexible sexuality in polyploid persimmon （D. kaki） according to establishment of epigenetic layers on OGI and MeGI.　Here, from the finding on the sex determination systems in persimmons, recent progresses of the studies on plant sexualities and their diversities among the species will be discussed.

Herbivore attack is one of the most important factors to decrease the agricultural production.　Many types of insecticide were developed and utilized to control the insect pests in the world.　Insecticides have been supporting the world agriculture.　However recently, it has become a big problem that many herbivores with insecticide resistance were appeared.　Especially, thrips developed highly resistance to many types of insecticide, and can cause serious problems in many crops, vegetables, fruits and flower plants.　This tiny and polyphagous pest insect is an also vector of tospoviruses, Therefore, both the feeding damage and the tospovirus disease caused by thrips are serious problems.　We have demonstrated that jasmonate （JA） dependent plant induced defense system restricts both thrips performance and preference.　JA treatment to the plants increases the thrips avoidance and controls the thrips behavior.　We also introduce our approach to use the JA analog, prohydrojasmon for thrips control.

When exposed to volatiles from herbivore-infested plants or those from artificially damaged plants, intact plants enhance their defense against herbivores.　This phenomenon is called plant-plant communication.　Here, we firstly address how plants receive volatile compounds.　Exposure of tomato plants to volatiles emitted from common cutworm-infested conspecifics lead to accumulation of the glycoside, （Z）-3-hexenyl vicianoside.　The aglycon is derived from airborne （Z）-3-hexenol emitted from infested plants, indicating that glycosylation is one of the receiving mechanisms of volatile alcohols in plants.　Next, we show the sensitivity.　Intermittent exposure （twice a week） of trace amounts （less than 140 pptV） of green leaf volatiles emitted by a freshly damaged Arabidopsis plant over 3 weeks results in the increased volatile production in undamaged neighboring plants.　The repeated exposure makes plants respond to subcritical amounts of chemical signals.　Thirdly, we show the results of field experiments.　In the soybean fields, half of the young stage soybean plants were exposed to volatiles from cut goldenrods, while the other half remained unexposed.　There was a significant reduction in the level of the total leaf damage on exposed soybean plants compared with unexposed ones.　The number of undamaged seeds and concentrations of isoflavones in the seeds from the exposed plants was significantly higher than that from unexposed ones.　These data indicate that soybean plants evaluate environments using cut goldenrod volatiles.

Weed control is essential for sugarcane production in Okinawa prefecture.　Production situation and weed status in sugarcane field are mentioned.　Bushkiller Cayratia tenuifolia has caused special weed problem in the southern part of Okinawa island.　Herbicides to control weeds are essential to prevent weed competition and losses in sugarcane production.

Why Monochoria vaginalis propagates in rice paddy field was investigated.　It was shown that nutrients such as amino acids and phosphate contained in rice hull accelerate the proliferation of bacteria which in turn digest the seed coat of Monochoria, facilitating its germination and hence propagation.