Laboratory of Horticultural Science

Plants accumulate as many as a million different metabolites (components), and the type of metabolites accumulated determines a crop's taste, aroma, color, and functionality. Mass Spectrometry (MS) is the technology used to distinguish and accurately analyze these metabolite molecules, with LC-MS and GC-MS being commonly used methods. However, analysis using LC-MS and GC-MS is complicated, laborious, and time-consuming, requiring steps like extraction, pre-treatment, and chromatographic separation using LC or GC.

We are utilizing novel mass spectrometry technologies, which we collectively call AI-MS, to conduct rapid and simple analysis of bioactive compounds in plants and insects. These technologies include APCDI-MS, which allows for the real-time mass analysis of volatile aromatic components (Volatile Organic Compounds: VOCs) simply by analyzing what evaporates from the sample, bypassing all of the aforementioned complicated steps. Another method is PESI-MS, which involves analyzing the sample in just a few minutes by simply pricking it with an ultrafine needle.

It has been revealed that the "catnip response," where cats play with the silver vine (matatabi), is a behavior where the cat rubs itself against the plant to cover its body with a compound called nepetalactol, thus repelling mosquitoes (link). The question then becomes: for what purpose did the silver vine begin synthesizing and accumulating nepetalactol?

We are using AI-MS and Omics technologies to clarify the mechanism of nepetalactol synthesis, accumulation, and emission in Actinidia species, and simultaneously, to reveal the physiological significance—the purpose for which the silver vine accumulates nepetalactol.

The entire genome sequences of many organisms, including horticultural crops, have been decoded, and the genetic information has been publicly released. However, unless this genetic information is organized by gene family and individual genes are assigned meaning (annotated), the valuable genomic information cannot be effectively utilized. We are organizing and annotating the information for gene families, specifically those related to transporters and transcription factors, in horticultural crops such as tomato, grape, and morning glory. By doing so, we are providing the fundamental information necessary for breeding and physiological research.

Genome editing using CRISPR/Cas9 was announced in 2012, leading to an explosive spread of genome editing technology. Just two years after the CRISPR/Cas9 announcement, in 2014, we began genome editing in tomatoes. By using genome editing to disrupt the function of an invertase inhibitor—a protein that puts the brakes on the translocation of sugar (sucrose) from leaves to fruits—we successfully developed a tomato with a 30% increase in sugar content, while hardly changing the size or yield of the fruit.

Furthermore, we have also succeeded in developing a unique, elongated, peanut-shaped tomato by using genome editing to disrupt the function of the transcription factor MYB3R, which normally acts to brake the cell cycle.

Grafting is an agricultural technique where two types of plants are combined (the rootstock for the root system and the scion for the above-ground part) to utilize the advantages of both. It is a technique that Japan is proud of, having been developed by the meticulous and dextrous Japanese people, and is now spreading globally.

However, the mechanism behind why grafts sometimes succeed and sometimes fail to connect, as well as the phenomenon of interaction between the rootstock and scion, remains largely unknown. We are utilizing Omics technologies to research the adhesion affinity of grafts and the communication between the rootstock and scion. We have also succeeded in developing a rootstock that doubles the sugar content of tomatoes and are currently advancing its practical application.

We are engaged in the development of flowers with unprecedented beautiful colors, unusual shapes, and extended vase life through genetic modification. To date, we have successfully developed morning glories and petunias with green flower color and long viewing periods, as well as petunias that accumulate the brightly colored pigment betalain.

Genetic modification requires not only the gene that controls the desired trait, but also a promoter to control the location and timing of gene expression, and enhancers and terminators to boost transcription and translation. We are working on developing petal-specific promoters that express genes only in the petals, as well as developing expression vectors that enhance transcription and translation.

How is genetic modification and genome editing performed in plants? While there is a simple method called "floral dip" for genetically modifying Arabidopsis thaliana (thale cress), performing genetic modification or genome editing in other plants requires laborious aseptic culture (sterile culture).

We have begun developing a method to induce genetic modification during the process of adventitious shoot regeneration from a cut leaf, thus obtaining genetically modified plants without the need for aseptic culture.

In modern agriculture, the year-round supply of horticultural crops (flowers and vegetables) is a crucial challenge. Therefore, in order to make flowers bloom or not bloom, or to make fruits set at the time we desire, it is necessary to make the crops sense the appropriate season.

We are focusing on "clock genes," which are the mechanism by which organisms perceive the seasons. We aim to control the expression rhythm of these clock genes using chemical control or genome editing to make flowers bloom or fruits set exactly when desired.

Why are fruits so sweet and delicious? Fruit juice is accumulated within the vacuoles of the cells. The vacuole accumulates high concentrations of substances related to taste, such as sugars, organic acids, and amino acids, as well as substances related to color, such as anthocyanins, related to nutrition, such as vitamins, and related to functionality, such as polyphenols.

For this reason, we consider the "fruit vacuole to be the most delicious, beautiful, and healthy organelle in the biological world." We are focusing our research on the factors involved in the accumulation of these substances into the vacuole, specifically the proton pumps, aquaporins, sugar transporters, organic acid transporters, and secondary metabolite transporters (ABC transporters, MATE).

Grapes are one of the most industrially important fruit crops globally, required for fresh consumption as well as for wine production. We are utilizing Omics technologies to study the synthesis of secondary metabolites in grape skins and cultured cells, focusing on the synthesis, accumulation, and regulation of anthocyanins (related to coloration) and resveratrol (a notable functional component). Recently, poor grape coloration caused by global warming has become a worldwide problem, and we are also conducting research on this issue.

Pear fruits contain "stone cells" (or grit cells) which cause a distinctive gritty texture. Stone cells are specialized cells that accumulate lignin. While many people in Japan enjoy the gritty texture of stone cells, many people in China dislike it.

We are advancing research on the formation mechanism and control of these stone cells through a joint study with Nanjing Agricultural University. We are using metabolomics to identify the stone cell-inducing factors that flow from the tree into the fruit, and simultaneously conducting chemical screening and chemical biology of stone cell-inducing compounds.