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  • Author or Editor: Tomoya Esumi x
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Japanese pear (Pyrus pyrifolia) and quince (Cydonia oblonga), both classified in the subfamily Maloideae, show differences in inflorescence architectures despite of the fact that they are genetically closely related. We previously isolated flowering related genes, LEAFY (LFY) and TERMINAL FLOWER 1 (TFL1) homologues, from these species and showed that they had two types of homologues for each gene. In this study, we examined the expression pattern of LFY and TFL1 homologues in these species by in situ hybridization and RT-PCR. The floral bud was dissected to small pieces under stereomicroscope; apical meristem, scales/bracts, pith, floral meristem, and inflorescence; and then used for RT-PCR. The LFY homologues were expressed in apical meristem and scales/bracts before the floral differentiation in both Japanese pear and quince. After floral differentiation, the expression was observed in floral meristem, scales/bracts and pith in both the species. The TFL1 homologues were strongly expressed in the apical meristem, but their expression was drastically decreased just before floral differentiation. It is considered that the decrease of expression of TFL1 homologues is a sign of floral initiation. The expression of TFL1 homologues was transiently increased at the beginning of floral differentiation in both species. Moreover, one of TFL1 homologues in Japanese pear was continuously expressed in the inflorescence part in the floral primordia, whereas expression of TFL1 homologues in quince almost completely disappeared after a solitary floral meristem was initiated. It was suggested that TFL1 homologues may also be involved in the inflorescence development of Japanese pear.

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In persimmon, plant regeneration from cultured cells usually takes place through adventitious bud formation. If somatic embryogenesis were possible, the efficiency of mass propagation and genetic engineering would be greatly improved. We attempted to induce somatic embryogenesis from immature embryos and plant regeneration from the induced embryos. Hypocotyls and cotyledons from immature ‘Fuyu’ and ‘Jiro’ seeds were cultured in the dark in Murashige and Skoog medium solidified with gellan gum and supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladenine (BA) at various concentrations. Callus formation started at ≈2 weeks of culture, and the callus formation rate was highest at 3 or 10 μm combinations of 2,4-D and BA. The initially formed calli gradually became brown or black from which white embryogenic calli (EC) appeared secondarily. After ≈8 weeks of culture, globular embryos were formed from these EC, and the formation proceeded until 20 weeks of culture. Formation of globular embryos was higher with ‘Fuyu’ than ‘Jiro’, especially with hypocotyls. When EC with globular embryos were transferred to fresh medium with no plant growth regulators, ≈70% developed to the torpedo-type embryo stage in 6 weeks. The torpedo-type embryos thus formed were germinated and rooted in agar medium with or without zeatin in several weeks without entering dormancy. After germination and rooting, the plantlets were transferred to the same medium and acclimatized for another 4 weeks. As the embryos germinated and rooted simultaneously, the plantlets were easy to grow in pots without transplanting shock. This is the first report on plant regeneration through somatic embryogenesis of persimmon.

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Fruit size is one of the most important traits that affect the economic value of fruit. In persimmon (Diospyros kaki Thunb.), somatic and bud-sport mutations that affect the fruit traits are frequently observed. Recently, a small-fruit mutant, ‘Totsutanenashi’ (TTN), was discovered in Japan as a bud-sport mutant of the leading cultivar Hiratanenashi (HTN). In this study, we investigated the morphological and physiological characteristics of TTN and HTN focusing on the tree architecture, fruit size, and the fruit flesh chemical composition. The objectives of the study were to evaluate the potential horticultural use of TTN and to characterize the differences between HTN and TTN. Both TTN and HTN are nonaploid plants, indicating that a difference in ploidy is not the cause of the small-fruit mutation. The vegetative growth of trees and tissue-cultured shoots of TTN was more compact than that of HTN. The floral organs of TTN appeared similar to those of HTN before flowering, but the TTN flowers opened earlier, resulting in smaller ovaries than in HTN flowers. The fruit size of TTN was consistently lower than that of HTN at all fruit developmental stages. TTN fruit had a higher sugar content and a higher proportion of sucrose to total sugars than HTN fruit. TTN fruits contained lower levels of secondary metabolites such as soluble tannins and ascorbate than HTN fruits. These results suggest that the fruit size mutation also affects the fruit biochemistry, leading to alterations in the fruit flesh composition. TTN may be a valuable genetic resource because compact trees require less labor and maintenance, and small, sweeter fruits may meet the various needs of consumers. The use of TTN in studies of the genetic control of fruit size is also discussed.

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Most commercial cultivars of japanese plum (Prunus salicina Lindl.) exhibit S-RNase-based gametophytic self-incompatibility (GSI), although some self-compatible (SC) cultivars exist. In this study, we characterized S-RNase and SFB, the pistil and pollen S determinants of the specificity of the GSI reaction, respectively, from four S-haplotypes, including a SC (Se ) and three SI (Sa , Sb , and Sc ) S-haplotypes of japanese plum. The genomic organization and structure of the SC Se-haplotype appear intact, because the relative transcriptional orientation of its S-RNase and SFB and their intergenetic distance are similar to those of the other three SI S-haplotypes of japanese plum and other Prunus L. species. Furthermore, there is no apparent defect in the DNA sequences of Se-RNase and SFBe . However, a series of transcriptional analyses, including real-time reverse transcriptase–polymerase chain reaction, showed that the Se-RNase transcript levels in the pistil are significantly lower than those of the Sa-, Sb-, and Sc-RNases, although transcripts of SFBa , SFBb , SFBc , and SFBe are present at similar levels in pollen. Furthermore, no Se-RNase spot was detected in two-dimensional polyacrylamide gel electrophoresis profiles of stylar extracts of the cultivars with the Se-haplotype. We discuss the possible molecular basis of SC observed with the Se -haplotype with special reference to the insufficient Se-RNase accumulation incited by the very low transcriptional level of Se-RNase in pistils.

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Most of the self-compatible (SC) cultivars of almond [Prunus dulcis (Mill.) D.A. Webb. syn. P. amygdalus Batsch] have the Sf haplotype. In this study, we cloned and characterized the S locus region of the Sf haplotype of SC ‘Lauranne’. The relative transcriptional orientation of SFBf and Sf-RNase and the physical distance between them are similar to those of other functional self-incompatible (SI) S haplotypes of Prunus, indicating that the genomic structure of the SC Sf haplotype appears to be intact. Although there is no apparent mutation in the coding sequence of SFBf , the Sf-RNase sequence in this study and previously reported Sf-RNase sequences show discrepancies. First, as opposed to previous indications, the ‘Lauranne’ Sf-RNase sequence encodes a histidine residue in place of a previously reported arginine residue in the conserved C2 region of Prunus S-RNase. Direct sequencing of the polymerase chain reaction products from the Sf-RNase of ‘Tuono’ confirmed that ‘Tuono’ Sf-RNase also encodes the histidine residue. We found another difference in the ‘Lauranne’ Sf-RNase sequence and other reported Sf-RNase sequences. Namely, ‘Lauranne’ Sf-RNase encodes a phenylalanine residue in place of a previously reported leucine residue in the conserved C5 region of Prunus S-RNase. This is also the case for ‘Tuono’ Sf-RNase. Expression analysis of Sf-RNase and SFBf by reverse transcriptase–polymerase chain reaction showed that Sf-RNase transcripts were barely detectable in pistil, whereas SFBf transcripts were accumulated at a similar level to the level that was observed with SFB of other functional SI S haplotypes of almond. We discuss the possible molecular mechanisms of SC observed with the Sf haplotype with special references to the expression of Sf-RNase.

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