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Dioecy, the presence of male and female flowers on distinct individuals, has evolved independently in multiple plant lineages, and the genes involved in this differential development are just starting to be uncovered in a few species. Here, we used genomic approaches to investigate this pathway in kiwifruits (genus Actinidia). Genome-wide cataloging of male-specific subsequences, combined with transcriptome analysis, led to the identification of a type-C cytokinin response regulator as a potential sex determinant gene in this genus. Functional transgenic analyses in two model systems, Arabidopsis thaliana and Nicotiana tabacum, indicated that this gene acts as a dominant suppressor of carpel development, prompting us to name it Shy Girl (SyGI). Evolutionary analyses in a panel of Actinidia species revealed that SyGI is located in the Y-specific region of the genome and probably arose from a lineage-specific gene duplication. Comparisons with the duplicated autosomal counterpart, and with orthologs from other angiosperms, suggest that the SyGI-specific duplication and subsequent evolution of cis-elements may have played a key role in the acquisition of separate sexes in this species.

The low photostability of fluorescent proteins is a limiting factor in many applications of fluorescence microscopy. Here we present StayGold, a green fluorescent protein (GFP) derived from the jellyfish Cytaeis uchidae . StayGold is over one order of magnitude more photostable than any currently available fluorescent protein and has a cellular brightness similar to mNeonGreen. We used StayGold to image the dynamics of the endoplasmic reticulum (ER) with high spatiotemporal resolution over several minutes using structured illumination microscopy (SIM) and observed substantially less photobleaching than with a GFP variant optimized for stability in the ER. Using StayGold fusions and SIM, we also imaged the dynamics of mitochondrial fusion and fission and mapped the viral spike proteins in fixed cells infected with severe acute respiratory syndrome coronavirus 2. As StayGold is a dimer, we created a tandem dimer version that allowed us to observe the dynamics of microtubules and the excitatory post-synaptic density in neurons. StayGold will substantially reduce the limitations imposed by photobleaching, especially in live cell or volumetric imaging. StayGold is over one order of magnitude more photostable than current fluorescent proteins

Floral morphology is a crucial trait that determines the commercial value of ornamental plants and pollinator preference. Scaevola aemula (Fan Flower) typically develops bilaterally symmetrical flowers, but a recessive mutant with a radially symmetrical flower (peloric) has been isolated from a breeding population. In the present study, we explored the molecular basis of the floral traits of S. aemula . We found a genetic-phenotypic association for the CYCLOIDEA (CYC) gene SaCYC2 , which is known as a regulatory gene for floral symmetry in various plants. The peloric flower line had a nonsense mutation immediately downstream of the start codon of SaCYC2 causing a loss of function. RNA-sequencing analysis revealed three paralogous CYC genes in S. aemula , but only SaCYC2 was preferentially expressed in the dorsal side of the petals. Moreover, we developed a co-dominant cleaved amplified polymorphic sequence (CAPS) marker based on the nonsense mutation to verify floral traits, thereby accelerating the selection and breeding of Scaevola spp. Our findings support the conserved function of CYC genes that determine aspects of floral morphology in Asteraceae.

Main ConclusionFor the first time, stone cells in pear and apple pedicel were studied. The lignification of the pedicel outer part was correlated with flesh, and the secondary cell wall biosynthesis genes were activated.Fruit pedicels act as bridges between the fruit and the shoot. They have secondary thickened cell walls that presumably function in mechanical support, water and nutrient transport. Stone cells are cells with a secondary cell wall thickening. In pears, yet not in apples, the stone cells affect the flesh texture. There have been few reports on stone cell formation in pear and apple pedicels; therefore, we studied these cells for the first time. The apple pedicel had few stone cells in the cortex. The formation of stone cells in pear continued until seven weeks after flowering (WAF), and the density was significantly higher than in apple. The stone cell formation degree (SFD) of pear was 3.6–7.1 times higher than that of apple. Total lignin and lignin non-condensed structure (G and S units) content in the pear pedicle outer part was 1.5–2.7 times higher than that of the apple at harvest. The SFD of the pedicel outer part had a positive correlation with the G and S units content of the flesh. The total lignin and G and S units content between flesh and the pedicel outer part were positively correlated. Correlation analysis revealed a positive relationship between fruit and pedicel formation of the stone cells. The WGCNA showed that NST3 was linked to NAC028, MYB46, CESA, POD, LAC, and VSR6. These genes were highly expressed in the outer part of the pear pedicel, while they were suppressed in that issue of the apple at 4 WAF.

The Japanese apricot ( Prunus mume ) is a popular fruit tree in Japan. However, the genetic factors associated with fruit trait variations are poorly understood. In this study, we investigated nine fruit-associated traits, including harvesting time, fruit diameter, fruit shape, fruit weight, stone (endocarp) weight, ratio of stone weight to fruit weight, and rate of fruit gumming, using 110 Japanese apricot accessions over four years. A genome-wide association study (GWAS) was performed for these traits and strong signals were detected on chromosome 6 for harvesting time and fruit diameters. These peaks were shown to undergo strong artificial selection during the differentiation of small-fruit cultivars. The genomic region defined by the GWAS and XP-nSL analyses harbored several candidate genes associated with plant hormone regulation. Furthermore, the alleles of small-fruit cultivars in this region were shown to have genetic proximity to some Chinese cultivars of P. mume . These results indicate that the small-fruit trait originated in China; after being introduced into Japan, it was preferred and selected by the Japanese people, resulting in the differentiation of small-fruit cultivars.

Key message Characterization of hybrid seed failure in Prunus provides insight into conserved or lineage-specific hybrid incompatibility mechanisms in plant species. Postzygotic hybrid incompatibility resulting from a cross between different species involves complex mechanisms occurring at various developmental stages. Embryo arrest, followed by seed abortion, is the first stage of such incompatibility reactions and inhibits hybrid seed development. In Prunus , a rosaceous woody species, some interspecific crosses result in fruit drop during the early stage of fruit development, in which inferior seed development may be accounted for the observed hybrid incompatibility. In this study, we investigated ovule development and the transcriptomes of developing ovules in inter-subgeneric crosses of Prunus . We conducted a cross of Prunus mume (subgenus Prunus ), pollinated by P. persica (subgenus Amygdalus ), and found that ovule and seed coat degeneration occurs before fruit drop. Transcriptome analysis identified differentially expressed genes enriched in several GO pathways, including organelle development, stimulus response, and signaling. Among these pathways, the organelle-related genes were actively regulated during ovule development, as they showed higher expression in the early stage of interspecific crosses and declined in the later stage, suggesting that the differential regulation of organelle function may induce the degeneration of hybrid ovules. Additionally, genes related to ovule and seed coat development, such as genes encoding AGL -like and auxin response, were differentially regulated in Prunus interspecific crosses. Our results provide histological and molecular information on hybrid seed abortion in Prunus that could be utilized to develop new hybrid crops. Additionally, we compared and discussed transcriptome responses to hybrid seed failure in Prunus and other plant species, which provides insight into conserved or lineage-specific hybrid incompatibility mechanisms in some plant species.

Hybridizations involving different species are often hindered because of incompatibility reactions. Although these reproductive barriers have been observed in many plant species, the underlying mechanisms remain to be comprehensively elucidated. In this study, we detected a hybridization barrier between apple (Malus × domestica) and pear (Pyrus spp.) belonging to different genera in the subtribe Malinae of the family Rosaceae. Pollination experiments revealed that Pyrus pyrifolia (Japanese pear) pollen is compatible with Malus pistils, whereas Pyrus communis (European pear) pollen is not. These results imply there is a distinct cross-(in)compatibility reaction occurring in Pyrus species. Based on the varying pollen tube behaviors among Pyrus species, genetic analysis was conducted to identify the genomic region responsible for the intergeneric barrier. Malus–Pyrus intergeneric hybrids were used to detect distorted segregation regions by combining genome sequencing and fine-scale genotyping data. We defined a single locus on chromosome 5, in which P. pyrifolia-derived alleles were exclusively inherited to the intergeneric hybrids from the Pyrus interspecific hybrid. Of the 235 genes in this genomic region, 80 exhibited a specific pollen-expression pattern, including genes involved in self-incompatibility reactions. These candidate genes are herein discussed regarding their possible functions related to reproductive isolation.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the disease COVID-19 can lead to serious symptoms, such as severe pneumonia, in the elderly and those with underlying medical conditions. While vaccines are now available, they do not work for everyone and therapeutic drugs are still needed, particularly for treating life-threatening conditions. Here, we showed nasal delivery of a new, unmodified camelid single-domain antibody (VHH), termed K-874A, effectively inhibited SARS-CoV-2 titers in infected lungs of Syrian hamsters without causing weight loss and cytokine induction. In vitro studies demonstrated that K-874A neutralized SARS-CoV-2 in both VeroE6/TMPRSS2 and human lung-derived alveolar organoid cells. Unlike other drug candidates, K-874A blocks viral membrane fusion rather than viral attachment. Cryo-electron microscopy revealed K-874A bound between the receptor binding domain and N-terminal domain of the virus S protein. Further, infected cells treated with K-874A produced fewer virus progeny that were less infective. We propose that direct administration of K-874A to the lung could be a new treatment for preventing the reinfection of amplified virus in COVID-19 patients.

The columnar trait in apple (Malus × domestica Borkh.) is characterized by short internodes, reduced branching, and increased spurs, which are labor-saving features useful for high-density planting. In this study, we used six segregating populations of a descendant of the columnar-type cultivar ‘Maypole’ and constructed a genetic linkage map for the columnar gene (Co). Based on the linkage map of the Co gene, contig sequences of the Co region between simple sequence repeat (SSR) markers CH03d11 and Hi01a03 of the apple genome were screened for SSR motifs. Amplification of 14 out of 26 newly designed SSR markers yielded fragments specifically linked to the Co gene. Genotyping of recombinants with the 14-marker set and five additional Co-linked markers delimited the Co region to a 530-kb region of the apple genome that overlap those found in previous studies in spite of the different genetic materials and backgrounds. Eight markers showed co-segregation with the Co locus. Genotypes of columnar cultivars/selections and normal-type cultivars were determined for four closely linked markers. For three markers, Co-linked fragments were generated not only from columnar-type cultivars but also from the ‘McIntosh’ and its normal-type offspring. In contrast, the Co-specific marker 29f1-JWl1r corresponded completely with the columnar trait in all cultivars and recombinants, indicating that this marker would be valuable for marker-assisted selection during columnar apple breeding.