In Arabidopsis thaliana, the three MADS box genes SEEDSTICK (STK), SHATTERPROOF1 (SHP1), and SHP2 redundantly regulate ovule development. Protein interaction studies have shown that a multimeric complex composed of the ovule identity proteins together with the SEPALLATA MADS domain proteins is necessary to determine ovule identity. Despite the extensive knowledge that has become available about these MADS domain transcription factors, little is known regarding the genes that they regulate. Here, we show that STK, SHP1, and SHP2 redundantly regulate VERDANDI (VDD), a putative transcription factor that belongs to the plant-specific B3 superfamily. The vdd mutant shows defects during the fertilization process resulting in semisterility. Analysis of the vdd mutant female gametophytes indicates that antipodal and synergid cell identity and/or differentiation are affected. Our results provide insights into the pathways regulated by the ovule identity factors and the role of the downstream target gene VDD in female gametophyte development.

Hirschsprung disease, or congenital megacolon, is characterized by aganglionosis of the terminal bowel, which leads to intestinal obstruction and chronic constipation. Several genes involved in the disease have been identified. In particular, haploinsufficiency of SOX10, which encodes a transcription factor, results in megacolon, often in combination with other disorders. Although Hirschsprung disease has been recognized as a neurocristopathy, the cellular mechanisms that lead to aganglionosis in affected individuals are unclear. Failure of mutant enteric progenitor cells to migrate into the gut, to survive, or to differentiate into appropriate cell types at the appropriate time and in correct numbers might contribute to the disease phenotype. In the present study, we use mice with a targeted deletion of Sox10 to study the etiology of Hirschsprung disease. We demonstrate that neural crest-derived enteric progenitors that are heterozygous for the Sox10 mutation colonize the proximal intestine and are unaffected in their survival capacity. However, unlike their wild-type counterparts, mutant enteric neural crest-derived cells are unable to maintain their progenitor state and acquire preneuronal traits, which results in a reduction of the progenitor pool size. Thus, the cells that normally colonize the hindgut are depleted in the Sox10 mutant, causing the distal bowel to become aganglionic.

SUMMARYPlant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20-90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.

Over 70 years ago, increased spontaneous mutation rates were observed in Drosophila spp. hybrids, but the genetic basis of this phenomenon is not well understood. The model plant Arabidopsis (Arabidopsis thaliana) offers unique opportunities to study the types of mutations induced upon hybridization and the frequency of their occurrence. Understanding the mutational effects of hybridization is important, as many crop plants are grown as hybrids. Besides, hybridization is important for speciation and its effects on genome integrity could be critical, as chromosomal rearrangements can lead to reproductive isolation. We examined the rates of hybridizationinduced point and frameshift mutations as well as homologous recombination events in intraspecific Arabidopsis hybrids using a set of transgenic mutation detector lines that carry mutated or truncated versions of a reporter gene. We found that hybridization alters the frequency of different kinds of mutations. In general, Columbia (Col) 3 Cape Verde Islands and Col 3 C24 hybrid progeny had decreased T→G and T→A transversion rates but an increased C→T transition rate. Significant changes in frameshift mutation rates were also observed in some hybrids. In Col 3 C24 hybrids, there is a trend for increased homologous recombination rates, except for the hybrids from one line, while in Col 3 Cape Verde Islands hybrids, this rate is decreased. The overall genetic distance of the parents had no influence on mutation rates in the progeny, as closely related accessions on occasion displayed higher mutation rates than accessions that are separated farther apart. However, reciprocal hybrids had significantly different mutation rates, suggesting parentof-origin-dependent effects on the mutation frequency.In plants, somatic mutations are an important source of genetic variability, which can, in principle, be passed on as heritable changes to the progeny of an individual (Baake and Gabriel, 1999). Plants have higher point mutation rates than animals (Kovalchuk et al., 2000) and do not have a fixed germline, such that there is a chance for somatic mutations to be transmitted to the next generation (Walbot and Evans, 2003). In contrast, animals cannot transmit somatic mutations to their progeny, as their germline cells are set aside early during development.Mutation rates have been estimated in several organisms, including bacteria and mammals (Kovalchuk et al., 2000). The easiest phenotype for estimating mutation rates in plants is chlorophyll deficiency or albinism. In barley (Hordeum vulgare), it was estimated that albino phenotypes can result from mutations in about 300 different nuclear genes (Klekowski, 1992). Mutations leading to chlorophyll deficiency in barley and buckwheat (Fagopyrum esculentum) occur at rates of 3.2 3 10 24 and 3.1 3 10 24 events per nuclear genome per generation, respectively. In long-lived red mangrove (Rhizophora mangle) plants, this rate was found to be 25 times higher, which led to the prediction that long-lived plants have higher mutation rates per...

BackgroundThe pollen tube (PT) serves as a model system for investigating plant cell growth and morphogenesis. Ultrastructural studies are indispensable to complement data from physiological and genetic analyses, yet an effective method is lacking for PTs of the model plant Arabidopsis thaliana.MethodsHere, we present reliable approaches for ultrastructural studies of Arabidopsis PTs, as well as an efficient technique for immunogold detection of cell wall epitopes. Using different fixation and embedding strategies, we show the amount of PT ultrastructural details that can be obtained by the different methods. ResultsDozens of cross-sections can be obtained simultaneously by the approach, which facilitates and shortens the time for evaluation. In addition to in vitro-grown PTs, our study follows the route of PTs from germination, growth along the pistil, to the penetration of the dense stylar tissue, which requires considerable mechanical forces. To this end, PTs have different strategies from growing between cells but also between the protoplast and the cell wall and even within each other, where they share a partly common cell wall. The separation of PT cell walls in an outer and an inner layer reported for many plant species is less clear in Arabidopsis PTs, where these cell wall substructures are connected by a distinct transition zone.ConclusionsThe major advancement of this method is the effective production of a large number of longitudinal and cross-sections that permits obtaining a detailed and representative picture of pollen tube structures in an unprecedented way. This is particularly important when comparing PTs of wild type and mutants to identify even subtle alterations in cytoarchitecture. Arabidopsis is an excellent plant for genetic manipulation, yet the PTs, several-times smaller compared to tobacco or lily, represent a technical challenge. This study reveals a method to overcome this problem and make Arabidopsis PTs more amenable to a combination of genetic and ultrastructural analyses.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1136-x) contains supplementary material, which is available to authorized users.