How plants grow up

A plant's lateral structures, such as leaves,branches and flowers, literally hinge on the shoot axis,making its integrity and growth fundamental to plant form.In all plants, subapical proliferation within the shoot tip displaces cells downward to extrude the cylindrical stem.Following the transition to flowering, many plants show extensive axial elongation associated with increased subapical proliferation and expansion. However, the cereal grasses also elongate their stems, called culms, due to activity within detached intercalary meristems which displaces cells upward, elevating the grain-bearing inflorescence. Variation in culm length within species is especially relevant to cereal crops, as demonstrated by the high-yielding semi-dwarfed cereals of the Green Revolution. Although previously understudied, recent renewed interest the regulation of subapical and intercalary growth suggests that control of cell division planes,boundary formation and temporal dynamics of differentiation, are likely critical mechanisms coordinating axial growth and development in plants.     

The microtubule catastrophe promoter Sentin delays stable kinetochore–microtubule attachment in oocytes

The critical step in meiosis is to attach homologous chromosomes to the opposite poles. In mouse oocytes, stable microtubule end-on attachments to kinetochores are not established until hours after spindle assembly, and phosphorylation of kinetochore proteins by Aurora B/C is responsible for the delay. Here we demonstrated that microtubule ends are actively prevented from stable attachment to kinetochores until well after spindle formation in Drosophila melanogaster oocytes. We identified the microtubule catastrophe-promoting complex Sentin-EB1 as a major factor responsible for this delay. Without this activity, microtubule ends precociously form robust attachments to kinetochores in oocytes, leading to a high proportion of homologous kinetochores stably attached to the same pole. Therefore, regulation of microtubule ends provides an alternative novel mechanism to delay stable kinetochore–microtubule attachment in oocytes.     

In vitro evaluation of native entomopathogenic fungi and neem (Azadiractha indica) extracts on Spodoptera frugiperda

The control of Spodoptera frugiperda is based on synthetic insecticides, so some alternatives are the use of entomopathogenic fungi (EF) and neem extract. The objective of the study was to evaluate in vitro effectiveness of native EF and neem extracts on S. frugiperda larvae. Six EF were identified by DNA sequencing of ITS regions from three EF (Fusarium solani, Metarrhizium robertsii, Nigrospora spherica and Penicillium citrinum). They were evaluated in concentrations of 1 × 10⁸ spores/ mL. In addition, a second bioassay was carried out evaluating only F. solani, M. robertsii and N. sphaerica and the addition of vegetable oil. On the other hand, extraction of secondary metabolites from neem seed (Azadirachta indica) was carried out by performing, mass (g) and solvent volume (mL ethanol and water) combinations, which were subjected to microwaves and ultrasound. Subsequently, these extracts were evaluated in concentrations of 3%, 4% and 5%. A survival analysis was performed for each of the bioassays. With respect to the results of the first bioassay, F. solani obtained a probability of survival of 0.476 on the seventh day, while in the second bioassay, M. robertsii obtained 0.488 survival probability. This suggests that the expected percentage of larvae that stay alive on the sixth day is 48.8%. However, in the evaluation of the neem extract the combination 1:12/70% to 4% caused 84% mortality of larvae. The use of native HE and neem extracts has potential for the control of S. frugiperda.     

Cytoplasmic Localization and Evolutionary Conservation of MEI-218, a Protein Required for Meiotic Crossing-over in Drosophila

During Drosophila oogenesis, the oocyte is formed within a 16-cell cyst immediately after four incomplete cell divisions. One of the primary events in oocyte development is meiotic recombination. Here, we report the intracellular localization of the MEI-218 protein that is specifically required for meiotic crossing-over. To understand the role of mei-218 in meiosis and to study the regulation of genes required for meiotic recombination, we characterized the expression pattern of its RNA and protein. Furthermore, we cloned and sequenced mei-218 from two other Drosophila species. The mei-218 RNA and protein have a similar expression pattern, appearing first in early meiotic prophase and then rapidly disappearing as prophase is completed. This pattern corresponds to a specific appearance of the mei-218 gene product in the region of the ovary where meiotic prophase occurs. Although mei-218 is required for 95% of all crossovers, the protein is found exclusively in the cytoplasm. Based on these results, we suggest that mei-218 does not have a direct role in recombination but rather regulates other factors required for the production of crossovers. We propose that mei-218 is a molecular link between oocyte differentiation and meiosis.     

Drosophila hold'em is required for a subset of meiotic crossovers and interacts with the dna repair endonuclease complex subunits MEI-9 and ERCC1

Three Drosophila proteins, ERCC1, MUS312, and MEI-9, function in a complex proposed to resolve double-Holliday-junction intermediates into crossovers during meiosis. We report here the characterization of hold'em (hdm), whose protein product belongs to a single-strand-DNA-binding superfamily of proteins. Mutations in hdm result in reduced meiotic crossover formation and sensitivity to the DNA-damaging agent methyl methanesulfonate. Furthermore, HDM physically interacts with both MEI-9 and ERCC1 in a yeast two-hybrid assay. We conclude that HDM, MEI-9, MUS312, and ERCC1 form a complex that resolves meiotic recombination intermediates into crossovers.     

Dual roles of Incenp crucial to the assembly of the acentrosomal metaphase spindle in female meiosis

Spindle formation in female meiosis differs from mitosis in many animals, as it takes place independently of centrosomes, and the molecular requirements of this pathway remain to be understood. Here, we report two crucial roles of Incenp, an essential subunit of the chromosomal passenger complex (the Aurora B complex), in centrosome-independent spindle formation in Drosophila female meiosis. First, the initial assembly of spindle microtubules is drastically delayed in an incenp mutant. This clearly demonstrates, for the first time, a crucial role for Incenp in chromosome-driven spindle microtubule assembly in living oocytes. Additionally, Incenp is necessary to stabilise the equatorial region of the metaphase I spindle, in contrast to mitosis, where the equivalent function becomes prominent after anaphase onset. Our analysis suggests that Subito, a kinesin-6 protein, cooperates with Incenp for this latter function, but not in microtubule assembly. We propose that the two functions of Incenp are part of the mechanisms that compensate for the lack of centrosomes during meiotic spindle formation.     

mei-P22 encodes a chromosome-associated protein required for the initiation of meiotic recombination in Drosophila melanogaster

Double-strand breaks (DSB) initiate meiotic recombination in a variety of organisms. Here we present genetic evidence that the mei-P22 gene is required for the induction of DSBs during meiotic prophase in Drosophila females. Strong mei-P22 mutations eliminate meiotic crossing over and suppress the sterility of DSB repair-defective mutants. Interestingly, crossing over in mei-P22 mutants can be restored to almost 50% of wild-type by X irradiation. In addition, an antibody-based assay was used to demonstrate that DSBs are not formed in mei-P22 mutants. This array of phenotypes is identical to that of mei-W68 mutants; mei-W68 encodes the Drosophila Spo11 homolog that is proposed to be an enzyme required for DSB formation. Consistent with a direct role in DSB formation, mei-P22 encodes a basic 35.7-kD protein, which, when examined by immunofluorescence, localizes to foci on meiotic chromosomes. MEI-P22 foci appear transiently in early meiotic prophase, which is when meiotic recombination is believed to initiate. By using an antibody to C(3)G as a marker for synaptonemal complex (SC) formation, we observed that SC is present before MEI-P22 associates with the chromosomes, thus providing direct evidence that the development of SC precedes the initiation of meiotic recombination. Similarly, we found that MEI-P22 foci did not appear in a c(3)G mutant in which SC does not form, suggesting that DSB formation is dependent on SC formation in Drosophila. We propose that MEI-P22 interacts with meiosis-specific chromosome proteins to facilitate DSB creation by MEI-W68.