Kazuhisa Kato

The treatment of plants with non-thermal atmospheric-pressure plasma impacts several aspects of plant life. However, the effects of long-term plasma irradiation on crop cultivation are not enough investigated. The purpose of the current study is to address this subject. The growth of tomato plants, the preservation status of harvested tomato fruits, and the microbial community on the surface of harvested tomato fruits were compared between 12 long-term plasma-irradiated plants and 12 air-irradiated plants with statistical analyses. The growth parameters (plant height, number of leaves and fruit bunches, SPAD value, and plant dry weight) of the plants that were periodically irradiated with plasma from the three-leaf stage to the green-enlarged-fruit stage, were the same as those of the air-irradiated controls. However, the preservation status of the tomato fruits harvested from the plasma-irradiated plants was improved in comparison with that of the fruits from the air-irradiated controls. Analysis of the microbiome on the surface of the fruit indicated that long-term plasma irradiation during cultivation promoted an increased bacterial diversity on the fruit surface. Thus, the effect of plasma irradiation on the diversification of microbial population dynamics on tomato fruit may be associated with an improved preservation status of harvested tomato fruits.

Dwarfing rootstocks are widely used in apple cultivation. We focused on adventitious rooting, crucial for vegetative propagation, and the phloem-to-xylem ratio, an indicator of dwarfing. Malus prunifolia and M. domestica ‘M.9’ were used as vigorous rootstocks with adventitious rooting ability and dwarf rootstocks without it, respectively. QTL analysis showed that QTLs for adventitious rooting (Cp) and the phloem-to-xylem ratio (Rb4) were located in the same genomic region, suggesting a potential relationship between the traits. The exon-intron structure, cDNA, and predicted amino acid sequences of the genes in the regions narrowed down by fine mapping for Cp were analyzed along with their expressions during cutting. Long transposable element-like insertions were found in MD17G1113200 and MD17G1113300 on the M. prunifolia genome unlike M. domestica. The gene product of MD17G1113300 in M. prunifolia was predicted to be 384 amino acids shorter than that of M. domestica in the C-terminal region, with different expression levels between the species during cutting. In MD17G1113900, functional amino acid substitutions and different expression levels during cutting were found between the species. When comparing other candidate genes for Cp between the species, different expression levels during cutting were found in MD17G1113400, MD17G1113500, and MD17G1113600. The physiological roles of these candidate genes and their relationships with adventitious rooting ability are discussed. Stereomicroscopic observation of the bases of cuttings revealed distinct morphological characteristics of M. prunifolia compared with M. domestica in terms of callus formation and rooting from lenticels and calli. Fully understanding the mechanisms determining adventitious root formation and developing highly accurate DNA markers are anticipated in the near future, and this paper will serve as a foundation for these achievements.

Ca2+ indicators, such as GCaMP6, have been primarily developed for animal research, and with limited applications in plants, they mainly target the vegetative organs of Arabidopsis and tobacco. Therefore, we focused on utilizing GCaMP6 in tomato fruit. Our observations revealed changes in fluorescence intensity upon cutting, as well as exposure to glutamate and EGTA, indicating that is possible to effectively measure the cellular Ca2+ concentration of GCaMP6-transformed tomato plants. The enhanced fluorescence intensity patterns under cold and salt stress imply that Ca2+ signals trigger responses to abiotic stress in fruit, with the salt stress response being organ-specific. Investigating the relationship between Ca2+ signaling and sugars, we found that glucose and fructose induce Ca2+ signaling in tomato fruit, with a response pattern dependent on sugar concentration. Moreover, a comparison of Ca2+ levels using corrected fluorescence intensity values during early fruit development, which is a critical stage for fruit physiology and the occurrence of disorders, revealed lower levels in the blossom end compared to the stem end 15 days after flowering. Using Ca2+ indicators in fruit has the potential elucidate the connection between Ca2+ and horticulturally important traits in fruits.

The effects of light quality on the flowering need to be investigated for the efficient use of light-emitting diodes (LEDs) in cut flower production because of the environmentally friendly features of LEDs. Assuming long-day treatments in cut flower production, we used Delphinium species, popular long-day plants, and treated the plants at night with relatively weak light to investigate the effects of light quality. We used reproductive experimental conditions with phytotrons and long-day treatments, mainly monochromatic light, to establish an experimental system to elucidate physiological and molecular mechanisms in the near future. Before investigating the effect of monochromatic light, we first performed a long-day treatment with a widely used white LED. A similar effect to the incandescent lamp on bolting was observed, suggesting the possibility that red or blue light, but not far-red light, are adequate to promote flowering from the spectra of both light sources. Next, long-day treatments were performed with LEDs emitting monochromatic blue, red, and far-red light. In the model plant Arabidopsis thaliana, flowering is well known to be promoted by far-red and blue light and inhibited by red light. However, long-day treatment with red light for Delphinium effectively promoted flowering. Treatment with far-red light, which shows an opposite flowering response to red light in A. thaliana, also promoted the flowering of Delphinium. As for blue light, the flower budding rate of D. grandiflorum reached 100%, and that of D. elatum was lower. Compared to far-red and blue lights, long-day treatment with red light did not negatively impact cut flower quality, including cut flower length and number of florets. Our results on light quality impact on flowering response will contribute to technology for regulating Delphinium flowering and potentially also lead to the elucidation of the mechanism of unique flowering promotion by red light.

Light quality affects plant growth and the functional component accumulation of fruits. However, there is little knowledge of the effects of light quality based on multiomics profiles. This study combined transcriptomic, ionomic, and metabolomic analyses to elucidate the effects of light quality on metabolism and gene expression in tomato fruit. Micro-Tom plants were grown under blue or red light-emitting diode light for 16 h daily after anthesis. White fluorescent light was used as a reference. The metabolite and element concentrations and the expression of genes markedly changed in response to blue and red light. Based on the metabolomic analysis, amino acid metabolism and secondary metabolite biosynthesis were active in blue light treatment. According to transcriptomic analysis, differentially expressed genes in blue and red light treatments were enriched in the pathways of secondary metabolite biosynthesis, carbon fixation, and glycine, serine, and threonine metabolism, supporting the results of the metabolomic analysis. Ionomic analysis indicated that the element levels in fruits were more susceptible to changes in light quality than in leaves. The concentration of some ions containing Fe in fruits increased under red light compared to under blue light. The altered expression level of genes encoding metal ion-binding proteins, metal tolerance proteins, and metal transporters in response to blue and red light in the transcriptomic analysis contributes to changes in the ionomic profiles of tomato fruit.

Fruit mass is an important factor for determining the yield of tomatoes (Solanum lycopersicum), with higher mass being an important objective. Most fruit traits, including fruit mass, are quantitative, and numerous quantitative trait loci (QTL) control these traits. Previous studies investigating tomato introgression lines (ILs) revealed several QTLs for fruit yield, and suggested that IL12-1 is a potential line to increase fruit mass. Our aim was to facilitate genetic studies of the diverse characteristics of wild relatives of tomato. Therefore, tomato ILs from a cross between Solanum pennellii and the cultivar S. lycopersicum ‘M82’ were used. ILs that carry a S. pennellii chromosome segment on chromosome 12 of ‘M82’ were evaluated further for fruit mass expansion and regulation. IL12-1-1, a subline of IL12-1, was found to produce large ripening fruits compared with ‘M82’, a phenotype that resulted in increased pericarp thicknesses. To investigate the physiological mechanisms contributing to the increased fruit mass of IL12-1-1, the cell counts of fruit pericarp tissues during fruit development were evaluated. Cell numbers of IL12-1-1 fruit pericarp at 20 days after flowering were higher than those of ‘M82’, a difference that most likely occurred during the cell division phase. In addition, the levels of the phytohormones auxin and cytokinin, which are known to be related to cell division of the fruit tissue, were higher in IL12-1-1 compared with ‘M82’. Therefore, differences in these phytohormones between ‘M82’ and IL12-1-1 may be affected by the number of cells in the pericarp tissues. Expression analysis of Solyc12g005250 (SlKLP) and Solyc12g005310 (SlGH3-15), which are located in the IL12-1-1 region of the S. pennellii chromosome, showed significant differences between ‘M82’ and IL12-1-1 during the cell division phase; a better understanding of IL12-1-1 cellular and molecular features can contribute to the breeding and increased production of tomato crops.

FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) is a blue-light receptor whose function is related to flowering promotion under long-day conditions in Arabidopsis thaliana. However, information about the physiological role of FKF1 in day-neutral plants and even the physiological role other than photoperiodic flowering is lacking. Thus, the FKF1 homolog SlFKF1 was investigated in tomato, a day-neutral plant and a useful model for plants with fleshy fruit. It was confirmed that SlFKF1 belongs to the FKF1 group by phylogenetic tree analysis. The high sequence identity with A. thaliana FKF1, the conserved amino acids essential for function, and the similarity in the diurnal change in expression suggested that SlFKF1 may have similar functions to A. thaliana FKF1. CONSTANS (CO) is a transcription factor regulated by FKF1 and is responsible for the transcription of genes downstream of CO. cis-Regulatory elements targeted by CO were found in the promoter region of SINGLE FLOWER TRUSS (SFT) and RIN, which are involved in the regulation of flowering and fruit ripening, respectively. The blue-light effects on SlFKF1 expression, flowering, and fruit lycopene concentration have been observed in this study and previous studies. It was confirmed in RNA interference lines that the low expression of SlFKF1 is associated with late flowering with increased leaflets and low lycopene concentrations. This study sheds light on the various physiological roles of FKF1 in plants.

Fruit trees need to overcome harsh winter climates to ensure perennially; therefore, they are strongly influenced by environmental stress. In the present study, we focused on the pear homolog PcLEA14 belonging to the unique 5C late embryogenesis abundant (LEA) protein group for which information is limited on fruit trees. PcLEA14 was confirmed to belong to this protein group using phylogenetic tree analysis, and its expression was induced by low-temperature stress. The seasonal fluctuation in its expression was considered to be related to its role in enduring overwinter temperatures, which is particularly important in perennially. Moreover, the function of PcLEA14 in low-temperature stress tolerance was revealed in transgenic Arabidopsis. Subsequently, the pear homolog of dehydration-responsive element-binding protein/C-repeat binding factor1 (DREB1), which is an important transcription factor in low-temperature stress tolerance and is uncharacterized in pear, was analyzed after bioinformatics analysis revealed the presence of DREB cis-regulatory elements in PcLEA14 and the dormancy-related gene, both of which are also expressed during low temperatures. Among the five PcDREBs, PcDREB1A and PcDREB1C exhibited similar expression patterns to PcLEA14 whereas the other PcDREBs were not expressed in winter, suggesting their different physiological roles. Our findings suggest that the low-temperature tolerance mechanism in overwintering trees is associated with group 5C LEA proteins and DREB1.

To elucidate the molecular mechanism of juvenility and annual flowering of fruit trees, FLOWERING LOCUS C (FLC), an integrator of flowering signals, was investigated in apple as a model. We performed sequence and expression analyses and transgenic experiments related to juvenility with annual flowering to characterize the apple FLC homologs MdFLC. The phylogenetic tree analysis, which included other MADS-box genes, showed that both MdFLC1 and MdFLC3 belong to the same FLC group. MdFLC1c from one of the MdFLC1 splice variants and MdFLC3 contain the four conserved motives of an MIKC-type MADS protein. The mRNA of variants MdFLC1a and MdFLC1b contain intron sequences, and their deduced amino acid sequences lack K- and C-domains. The expression levels of MdFLC1a, MdFLC1b, and MdFLC1c decreased during the flowering induction period in a seasonal expression pattern in the adult trees, whereas the expression level of MdFLC3 did not decrease during that period. This suggests that MdFLC1 is involved in flowering induction in the annual growth cycle of adult trees. In apple seedlings, because phase change can be observed in individuals, seedlings can be used for analysis of expression during phase transition. The expression levels of MdFLC1b, MdFLC1c, and MdFLC3 were high during the juvenile phase and low during the transitional and adult phases. Because the expression pattern of MdFLC3 suggests that it plays a specific role in juvenility, MdFLC3 was subjected to functional analysis by transformation of Arabidopsis. The results revealed the function of MdFLC3 as a floral repressor. In addition, MdFT had CArG box-like sequences, putative targets for the suppression of flowering by MdFLC binding, in the introns and promoter regions. These results indicate that apple homologs of FLC, which might play a role upstream of the flowering signals, could be involved in juvenility as well as in annual flowering. Apples with sufficient genome-related information are useful as a model for studying phenomena unique to woody plants such as juvenility and annual flowering.