How do 'housekeeping' genes control organogenesis?--Unexpected new findings on the role of housekeeping genes in cell and organ differentiation.

In recent years, an increasing number of mutations in what would appear to be 'housekeeping genes' have been identified as having unexpectedly specific defects in multicellular organogenesis. This is also the case for organogenesis in seed plants. Although it is not surprising that loss-of-function mutations in 'housekeeping' genes result in lethality or growth retardation, it is surprising when (1) the mutant phenotype results from the loss of function of a 'housekeeping' gene and (2) the mutant phenotype is specific. In this review, by defining housekeeping genes as those encoding proteins that work in basic metabolic and cellular functions, we discuss unexpected links between housekeeping genes and specific developmental processes. In a surprising number of cases housekeeping genes coding for enzymes or proteins with functions in basic cellular processes such as transcription, post-transcriptional modification, and translation affect plant development.

Dynamic-module redundancy confers robustness to the gene regulatory network involved in hair patterning of Arabidopsis epidermis.

Redundancy among dynamic modules is emerging as a potentially generic trait in gene regulatory networks. Moreover, module redundancy could play an important role in network robustness to perturbations. We explored the effect of dynamic-module redundancy in the networks associated to hair patterning in Arabidopsis root and leaf epidermis. Recent studies have put forward several dynamic modules belonging to these networks. We defined these modules in a discrete dynamical framework that was previously reported. Then, we addressed whether these modules are sufficient or necessary for recovering epidermal cell types and patterning. After defining two quantitative estimates of the system's robustness, we also compared the robustness of each separate module with that of a network coupling all the leaf or root modules. We found that, considering certain assumptions, all the dynamic modules proposed so far are sufficient on their own for pattern formation, but reinforce each other during epidermal development. Furthermore, we found that networks of coupled modules are more robust to perturbations than single modules. These results suggest that dynamic-module redundancy might be an important trait in gene regulatory networks and point at central questions regarding network evolution, module coupling, pattern robustness and the evolution of development.

Recent achievements and trends in experimental plant biology.

Between 21 and 25 September 2009, Krakow hosted the 4th Conference of the Polish Society of Experimental Plant Biology, co-organized with the Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, and supported by the Biochemical Society. The aim of the conference was to present and discuss the most important topics in different disciplines of plant experimental science as well as to facilitate the interaction and co-operation between scientists. To achieve this goal, about 30 top specialists in various areas of plant biology were invited to give plenary lectures in the following sessions: Plant structure and development; Plant-microbial interactions; Mitochondria and chloroplasts in cell metabolism; Stress tolerance in plants; Structural and functional organization of plant genomes; Mutants in developmental and metabolic studies; Secondary metabolites as pharmaceutics and nutraceutics; Plant membranes; and Integrating plant functions via signalling molecules: molecular mechanisms. Some of the main problems highlighted in the plenary lectures are briefly summarized in the present paper. Two poster sessions enabled a discussion of over 200 posters presented. The conference had an international character, its official language was English, and among the more than 350 participants, about 60 were from abroad. Several plenary lectures were prepared as short review papers and they are published in this issue of Biochemical Society Transactions.

The role of chemical dynamics in plant morphogenesis(1).

In biological development, the generation of shape is preceded by the spatial localization of growth factors. Localization, and how it is maintained or changed during the process of growth, determines the shapes produced. Mathematical models have been developed to investigate the chemical, mechanical and transport properties involved in plant morphogenesis. These synthesize biochemical and biophysical data, revealing underlying principles, especially the importance of dynamics in generating form. Chemical kinetics has been used to understand the constraints on reaction and transport rates to produce localized concentration patterns. This approach is well developed for understanding de novo pattern formation, pattern spacing and transitions from one pattern to another. For plants, growth is continual, and a key use of the theory is in understanding the feedback between patterning and growth, especially for morphogenetic events which break symmetry, such as tip branching. Within the context of morphogenetic modelling in general, the present review gives a brief history of chemical patterning research and its particular application to shape generation in plant development.

The meristem-to-organ boundary: more than an extremity of anything.

In plant shoot meristems, cells with indeterminate fate are separated from determinate organ founder cells by morphological boundaries. Organ founder cells are selected at sites of auxin accumulation. Auxin is channeled between cells via efflux carrier proteins, but influx carriers are needed to concentrate auxin in the outer meristem layer. The genetic programmes executed by organs and meristems are established by mutual repression of transcription factors, involving the sequestration of enhancer elements into DNA loops. Boundary cells play a dual role in separating and maintaining meristem and organ domains, and express unique genes that reduce cell division and auxin efflux carrier activity, but activate meristematic gene expression. Boundary positions depend on signals emitted from indeterminate cells at the meristem center.

[Cell elongation as an inseparable component of growth in terrestrial plants].

The review is dedicated to the role of cell elongation in plant growth and morphogenesis. The ratios of cell division to elongation, cell competence for the initiation of elongation, main features of the metabolism of elongating cells, and physiological processes realizing elongation have been considered on the examples of seed germination and growth of roots, stems, and leaves. A special attention was paid to the vacuole as a specific feature of plant cells, pathways of its formation, and its role in maintenance of ion and water homeostasis in the elongating cell. The plant can modify its morphology according to changes in the environmental conditions via cell elongation.

Proteomic dissection of plant development.

Plant development is controlled by complex endogenous genetic programs and responses to environmental cues. Proteome analyses have recently been introduced to plant biology to identify proteins instrumental in these developmental processes. To date most plant proteome studies have been employed to generate reference maps of the most abundant soluble proteins of plant organs at a defined developmental stage. However, proteomics is now also utilized for genetic studies comparing the proteomes of different plant genotypes, for physiological studies analyzing the influences of exogenous signals on a particular plant organ, and developmental studies investigating proteome changes during development. Technical advances are now beginning to allow a proteomic dissection of individual cell types, thus greatly increasing the information revealed by proteome analyses.

Characterization of three Rop GTPase genes of alfalfa (Medicago sativa L.).

Three cDNA clones coding for Medicago sativa Rop GTPases have been isolated. The represented genes could be assigned to various linkage groups by genetic mapping. They were expressed in all investigated plant organs, although at different level. Relative gene expression patterns in response to Sinorhizobium infection of roots as well as during somatic embryogenesis indicated their differential participation in these processes. DNA sequences coding for altogether six different Medicago sp. Rop GTPases could be identified in sequence databases. Based on their homology to each other and to their Arabidopsis counterparts, a unified nomenclature is suggested for Medicago Rop GTPases.

MicroRNA regulation of NAC-domain targets is required for proper formation and separation of adjacent embryonic, vegetative, and floral organs.

BACKGROUND: MicroRNAs (miRNAs) are approximately 21 nucleotide (nt) RNAs that regulate gene expression in plants and animals. Most known plant miRNAs target transcription factors that influence cell fate determination, and biological functions of miRNA-directed regulation have been reported for four of 15 known microRNA gene families: miR172, miR159, miR165, and miR168. Here, we identify a developmental role for miR164-directed regulation of NAC-domain genes, which encode a family of transcription factors that includes CUP-SHAPED COTYLEDON1 (CUC1) and CUC2. RESULTS: Expression of a miR164-resistant version of CUC1 mRNA from the CUC1 promoter causes alterations in Arabidopsis embryonic, vegetative, and floral development, including cotyledon orientation defects, reduction of rosette leaf petioles, dramatically misshapen rosette leaves, one to four extra petals, and one or two missing sepals. Reciprocally, constitutive overexpression of miR164 recapitulates cuc1 cuc2 double mutant phenotypes, including cotyledon and floral organ fusions. miR164 overexpression also leads to phenotypes not previously observed in cuc1 cuc2 mutants, including leaf and stem fusions. These likely reflect the misregulation of other NAC-domain mRNAs, including NAC1, At5g07680, and At5g61430, for which miR164-directed cleavage products were detected. CONCLUSIONS: These results demonstrate that miR164-directed regulation of CUC1 is necessary for normal embryonic, vegetative, and floral development. They also show that proper miR164 dosage or localization is required for separation of adjacent embryonic, vegetative, and floral organs, thus implicating miR164 as a common regulatory component of the molecular circuitry that controls the separation of different developing organs and thereby exposes a posttranscriptional layer of NAC-domain gene regulation during plant development.

Fine mapping of the parthenocarpic fruit ( pat) mutation in tomato.

The parthenocarpic fruit ( pat) gene of tomato is a recessive mutation conferring parthenocarpy, which is the capability of a plant to set seedless fruits in the absence of pollination and fertilization. Parthenocarpic mutants offer a useful method to regulate fruit production and a suitable experimental system to study ovary and fruit development. In order to map the Pat locus, two populations segregating from the interspecific cross Lycopersicon esculentum x Lycopersicon pennellii were grown, and progeny plants were classified as parthenocarpic or wild-type by taking into account some characteristic aberrations affecting mutant anthers and ovules. Through bulk segregant analysis, we searched for both random and mapped AFLPs linked to the target gene. In this way, the Pat locus was assigned to the long arm of chromosome 3, as also confirmed by the analysis of a set of L. pennellii substitution and introgression lines. Afterwards, the Pat position was refined by using simple sequence repeats (SSRs) and conserved ortholog set (COS) markers mapping in the target region. The tightest COSs were converted into CAPS or SCAR markers. At present, two co-dominant SCAR markers encompassing a genetic window of 1.2 cM flank the Pat locus. Considering that these markers are orthologous to Arabidopsis genes, a positional cloning exploiting the tomato- Arabidopsis microsynteny seems to be a short-term objective.

Three-dimensional progression of programmed death in the rice coleoptile.

Plant death during development is a highly orchestrated process at the cellular, tissue, organ, and whole-plant levels. The process toward death is endogenously programmed in plants. With our original approach called "three-dimensional analysis" using the rice coleoptile, we revealed detailed morphological alterations in the progression of senescence and programmed cell death involved in the air space (aerenchyma) formation at both tissue and cellular levels. Although these two types of cell death exhibited a distinct pattern of progression at the tissue level, the set of intracellular events was highly conserved. From those comprehensive investigations, we hypothesized that the identical program of death functions in each process of cell death, and that the initiation and progression of cell death is highly regulated by the environmental input.

Microautoradiographic localisation of a glucosinolate precursor to specific cells in Brassica napus L. embryos indicates a separate transport pathway into myrosin cells.

The in-situ localisation of a desulpho-glucosinolate precursor has been studied by microautoradiography of cryo-sections from immature seeds and pods of the high-glucosinolate Brassica napus L. cv. Argentine collected 23 days after pollination. After feeding with the tritium-labelled glucosinolate precursor [4,5-3H](beta-D-glucopyranosyl)-4-pentenethiohydroxamic acid, embryo radicles, cotyledons and pod-wall were frozen in liquid nitrogen. Cryotome sections were freeze-dried and coated with nuclear emulsion autoradiographic film. A distinct pattern of radioactivity derived from the glucosinolate precursor was found in specific cells in both radicle and cotyledons. In contrast, the labelling in pod walls was not cell specific, but general at the inner side of the pod wall. The results show that the glucosinolate/desulphoglucosinolate was localised in specific cells, in a pattern resembling that of myrosin cells known to contain myrosinase (EC 3.2.3.1). In addition [4,5-3H](beta-D-glucopyranosyl)-4-pentenethiohydroxamic acid was fed to immature seeds and pods of B. napus and a quantitative incorporation into 2-hydroxy-3-butenylglucosinolate and 3-butenyl-glucosinolate was observed. When [4,5-3H](beta-D-glucopyranosyl)-4-pentenethiohydroxamic acid was fed to 4-day-old seedlings the label was taken up by all tissues. We propose a model in which glucosinolate/desulphoglucosinolates are transported to myrosin cells to participate in the myrosinase-glucosinolate multifunctional defence system.

The parthenocarpic fruit (pat) mutant of tomato (Lycopersicon esculentum Mill.) sets seedless fruits and has aberrant anther and ovule development.

Among the different sources of genetic parthenocarpy described in tomato, the mutation referred to as parthenocarpic fruit (pat) is of particular interest because of its strong expressivity and because it confers earlier ripening, higher fruit set and enhanced fruit quality. As a pleiotropic effect, pat flowers have aberrantly developing androecia and reduced male and female fertility. In this work we extend the early description of the pat phenotype by investigating the expression of parthenocarpy in three different environments and by using light and scanning electron microscopy to analyse the development of male and female floral organs. The degree of parthenocarpy was high in the three experimental environments and was characterised by a precocious initiation of ovary growth to pre-anthesis floral stages. Aberrations in anther development were evident at flower bud stages and resulted in shorter, irregular and teratoid organs. Ectopic production of carpel-like structures bearing external ovules was evident in the most severely altered androecia. Analysis of ovule development revealed that a fraction of pat ovules becomes aberrant from very early stages, having defective integument growth. Meiosis was irregular in aberrant ovules and megaspore or gamete production was severely hampered. The described pat syndrome suggests that parthenocarpy in this mutant could be a secondary effect of a gene controlling, at early stages, organ identity and development.

Pollen and ovule development in Arabidopsis thaliana under spaceflight conditions.

The development of pollen and ovules in Arabidopsis thaliana on the space shuttle 'Endeavour' (STS-54) was investigated. Plants were grown on nutrient agar for 14 days prior to loading into closed plant growth chambers that received light and temperature control inside the Plant Growth Unit flight hardware on the shuttle middeck. After 6 days in spaceflight the plants were retrieved and immediately dissected and processed for light and electron microscope observation. Reproductive development aborted at an early stage. Pistils were collapsed and ovules inside were seen to he empty. No viable pollen was observed from STS-54 plants; young microspores were deformed and empty. At a late stage, the cytoplasm of the pollen contracted and became disorganized, but the pollen wall developed and the exine appeared normal. The tapetum in the flight flowers degenerated at early stages. Ovules from STS-54 flight plants stopped growing and the integuments and nucellus collapsed and degenerated. The megasporocytes appeared abnormal and rarely underwent meiosis. Apparently they enlarged, or occasionally produced a dyad or tetrad, to assume the form of a female gametophyte with the single nucleus located in an egglike cell that lacks a cell wall. Synergids, polar nuclei, and antipodals were not observed. The results demonstrate the types of lesions occurring in plant reproductive material under spaceflight conditions.

Peculiarities of genital organ formation in Arabidopsis thaliana (L) Heynh. under spaceflight conditions.

An experiment was carried out ahoard the Salyut 6 research orbital station on Arabidopsis thaliana cultivations. The seeds were sprouted in the Svetoblok 1 device which provides for plant growth in the agar medium under sterile conditions and at 4000 lux illumination. The experimental plants, as well as the controls, reached approximately the same developmental stages: both flowered and began to bear fruit. A microscopic examination of the generative organs in the control and experimental plants shows that in normally formed (by appearance) flower buds and flowers of the experimental plants, as distinct from the controls, there were no fertile elements of the adroecium and gynoecium. Degeneration of the latter occurred at different stages of generative organ development. Possible reasons for this phenomenon in plants grown under weightless conditions are considered.