SummaryDownregulation of the transcription factor AtMYB103 using transgenic technology results in early tapetal degeneration and pollen aberration during anther development in Arabidopsis thaliana. This paper describes the functional analysis of the AtMYB103 gene in three knock-out mutants. Two male sterile mutants, ms188-1 and ms188-2, were generated by ethyl-methane sulfonate (EMS) mutagenesis. A map-based cloning approach was used, and ms188 was mapped to a 95.8-kb region on chromosome 5 containing an AtMYB103 transcription factor. Sequence analysis revealed that ms188-1 had a pre-mature stop codon in the AtMYB103 coding region, whereas ms188-2 had a CCT fi CTT base-pair change in the first exon of AtMYB103, which resulted in the replacement of a proline by a leucine residue in the R2R3 domain. The third mutant, an AtMYB103 transposon-tagging line, also showed a male sterile phenotype. Allelism tests indicated that MS188 and AtMYB103 belong to the same locus. Cytological observation revealed defective tapetum development and altered callose dissolution in ms188 plants. Additionally, most of the microspores in mature anthers were degraded and surviving microspores lacked exine. AtMYB103 encoded an R2R3 MYB protein that is predominantly located in the nucleus. Real-time RT-PCR analysis indicated that the callase-related gene A6 was regulated by AtMYB103. Expression of the exine formation gene MS2 was not detected in mutant anthers. These results implicate that AtMYB103 plays an important role in tapetum development, callose dissolution and exine formation in A. thaliana anthers.

Spinach is an important leafy vegetable enriched with multiple necessary nutrients. Here we report the draft genome sequence of spinach (Spinacia oleracea, 2n=12), which contains 25,495 protein-coding genes. The spinach genome is highly repetitive with 74.4% of its content in the form of transposable elements. No recent whole genome duplication events are observed in spinach. Genome syntenic analysis between spinach and sugar beet suggests substantial inter- and intra-chromosome rearrangements during the Caryophyllales genome evolution. Transcriptome sequencing of 120 cultivated and wild spinach accessions reveals more than 420 K variants. Our data suggests that S. turkestanica is likely the direct progenitor of cultivated spinach and spinach domestication has a weak bottleneck. We identify 93 domestication sweeps in the spinach genome, some of which are associated with important agronomic traits including bolting, flowering and leaf numbers. This study offers insights into spinach evolution and domestication and provides resources for spinach research and improvement.

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Tomato is a major vegetable crop that has tremendous popularity. However, viral disease is still a major factor limiting tomato production. Here, we report the tomato virome identified through sequencing small RNAs of 170 field-grown samples collected in China. A total of 22 viruses were identified, including both well-documented and newly detected viruses. The tomato viral community is dominated by a few species, and they exhibit polymorphisms and recombination in the genomes with cold spots and hot spots. Most samples were coinfected by multiple viruses, and the majority of identified viruses are positive-sense single-stranded RNA viruses. Evolutionary analysis of one of the most dominant tomato viruses, (TYLCV), predicts its origin and the time back to its most recent common ancestor. The broadly sampled data have enabled us to identify several unreported viruses in tomato, including a completely new virus, which has a genome of ∼13.4 kb and groups with aphid-transmitted viruses in the genus Although both DNA and RNA viruses can trigger the biogenesis of virus-derived small interfering RNAs (vsiRNAs), we show that features such as length distribution, paired distance, and base selection bias of vsiRNA sequences reflect different plant Dicer-like proteins and Argonautes involved in vsiRNA biogenesis. Collectively, this study offers insights into host-virus interaction in tomato and provides valuable information to facilitate the management of viral diseases. Tomato is an important source of micronutrients in the human diet and is extensively consumed around the world. Virus is among the major constraints on tomato production. Categorizing virus species that are capable of infecting tomato and understanding their diversity and evolution are challenging due to difficulties in detecting such fast-evolving biological entities. Here, we report the landscape of the tomato virome in China, the leading country in tomato production. We identified dozens of viruses present in tomato, including both well-documented and completely new viruses. Some newly emerged viruses in tomato were found to spread fast, and therefore, prompt attention is needed to control them. Moreover, we show that the virus genomes exhibit considerable degree of polymorphisms and recombination, and the virus-derived small interfering RNA (vsiRNA) sequences indicate distinct vsiRNA biogenesis mechanisms for different viruses. The Chinese tomato virome that we developed provides valuable information to facilitate the management of tomato viral diseases.

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Background: Two major NADPH dehydrogenase complexes, NDH-1L and NDH-1M, have been identified in cyanobacteria. Results: NdhP is localized in the NDH-1L complex, and absence of this subunit or its C-terminal tail disassembled NDH-1L to NDH-1M. Conclusion: C terminus of NdhP is essential to stabilize the NDH-1L complex. Significance: Our results provide novel insights into the assembly and stabilization of NDH-1L complex.

Spinach is a nutritious leafy vegetable belonging to the family Chenopodiaceae. Here we report a high-quality chromosome-scale reference genome assembly of spinach and genome resequencing of 305 cultivated and wild spinach accessions. Reconstruction of ancestral Chenopodiaceae karyotype indicates substantial genome rearrangements in spinach after its divergence from ancestral Chenopodiaceae, coinciding with high repeat content in the spinach genome. Population genomic analyses provide insights into spinach genetic diversity and population differentiation. Genome-wide association studies of 20 agronomical traits identify numerous significantly associated regions and candidate genes for these traits. Domestication sweeps in the spinach genome are identified, some of which are associated with important traits (e.g., leaf phenotype, bolting and flowering), demonstrating the role of artificial selection in shaping spinach phenotypic evolution. This study provides not only insights into the spinach evolution and domestication but also valuable resources for facilitating spinach breeding.

Purpose -The purpose of this paper is to investigate whether managerial ownership affects the association between shareholder rights and the cost of equity capital.Design/methodology/approach -Prior literature has shown that strong shareholder rights are associated with a lower level of cost of equity capital. This paper empirically tests the interaction between managerial ownership and shareholder rights on affecting the cost of equity capital, using Gompers et al.'s governance score and Ohlson and Juettner-Nauroth's estimate of cost of equity capital. To mitigate the endogeneity arising from other governance variables affecting both shareholder rights and the cost of equity capital, the paper adopts both OLS and two-stage regression.Findings -The results indicate that managerial ownership aligns managers' interests with those of shareholders, leading to a lesser degree of agency problems and lower cost of equity capital. Furthermore, the evidence suggests that managerial ownership could substitute for shareholder rights in affecting the cost of equity capital, making strong shareholder rights less important in a high managerial ownership setting.Research limitations/applications -Findings in this paper suggest that firms need to consider the interaction between managerial ownership and shareholder rights in designing their governance structure to minimize their cost of equity capital.Originality/value -This paper reveals the interaction between two major governance variables in affecting firm valuation.