Cytokinesis is the division of the cytoplasm and its separation into two daughter cells. Cell plate growth and cytokinesis appear to require callose, but direct functional evidence is still lacking. To determine the role of callose and its synthesis during cytokinesis, we identified and characterized mutants in many members of the GLUCAN SYNTHASE-LIKE (GSL; or CALLOSE SYNTHASE) gene family in Arabidopsis (Arabidopsis thaliana). Most gsl mutants (gsl1-gsl7, gsl9, gsl11, and gsl12) exhibited roughly normal seedling growth and development. However, mutations in GSL8, which were previously reported to be gametophytic lethal, were found to produce seedlings with pleiotropic defects during embryogenesis and early vegetative growth. We found cell wall stubs, two nuclei in one cell, and other defects in cell division in homozygous gsl8 insertional alleles. In addition, gsl8 mutants and inducible RNA interference lines of GSL8 showed reduced callose deposition at cell plates and/or new cell walls. Together, these data show that the GSL8 gene encodes a putative callose synthase required for cytokinesis and seedling maturation. In addition, gsl8 mutants disrupt cellular and tissue-level patterning, as shown by the presence of clusters of stomata in direct contact and by islands of excessive cell proliferation in the developing epidermis. Thus, GSL8 is required for patterning as well as cytokinesis during Arabidopsis development.
Many recent studies have demonstrated that several known and unknown viruses infect many horticultural plants. However, the elucidation of a viral population and the understanding of the genetic complexity of viral genomes in a single plant are rarely reported. Here, we conducted metatranscriptome analyses using six different peach trees representing six individual peach cultivars. We identified six viruses including five viruses in the family Betaflexiviridae and a novel virus belonging to the family Tymoviridae as well as two viroids. The number of identified viruses and viroids in each transcriptome ranged from one to six. We obtained 18 complete or nearly complete genomes for six viruses and two viroids using transcriptome data. Furthermore, we analyzed single nucleotide variations for individual viral genomes. In addition, we analyzed the amount of viral RNA and copy number for identified viruses and viroids. Some viruses or viroids were commonly present in different cultivars; however, the list of infected viruses and viroids in each cultivar was different. Taken together, our study reveals the viral population in a single peach tree and a comprehensive overview for the diversities of viral communities in different peach cultivars.
The cell wall and extracellular matrix in higher plants include secreted proteins that play critical roles in a wide range of cellular processes, such as structural integrity and biogenesis. Compared with the intensive cell wall proteomic studies in Arabidopsis, the list of cell wall proteins identified in monocot species is lacking. Therefore, we conducted a large-scale proteomic analysis of secreted proteins from rice. Highly purified secreted rice proteins were obtained from the medium of a suspension of callus culture and were analyzed with multidimensional protein identification technology (MudPIT). As a result, we could detect a total of 555 rice proteins by MudPIT analysis. Based on bioinformatic analyses, 27.7% (154 proteins) of the identified proteins are considered to be secreted proteins because they possess a signal peptide for the secretory pathway. Among the 154 identified proteins, 27% were functionally categorized as stress response proteins, followed by metabolic proteins (26%) and factors involved in protein modification (24%). Comparative analysis of cell wall proteins from Arabidopsis and rice revealed that one third of the secreted rice proteins overlapped with those of Arabidopsis. Furthermore, 25 novel rice-specific secreted proteins were found. This work presents the large scale of the rice secretory proteome from culture medium, which contributes to a deeper understanding of the rice secretome.
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