A Rapid Pipeline for Pollen- and Anther-Specific Gene Discovery Based on Transcriptome Profiling Analysis of Maize Tissues

Recently, crop breeders have widely adopted a new biotechnology-based process, termed Seed Production Technology (SPT), to produce hybrid varieties. The SPT does not produce nuclear male-sterile lines, and instead utilizes transgenic SPT maintainer lines to pollinate male-sterile plants for propagation of nuclear-recessive male-sterile lines. A late-stage pollen-specific promoter is an essential component of the pollen-inactivating cassette used by the SPT maintainers. While a number of plant pollen-specific promoters have been reported so far, their usefulness in SPT has remained limited. To increase the repertoire of pollen-specific promoters for the maize community, we conducted a comprehensive comparative analysis of transcriptome profiles of mature pollen and mature anthers against other tissue types. We found that maize pollen has much less expressed genes (>1 FPKM) than other tissue types, but the pollen grain has a large set of distinct genes, called pollen-specific genes, which are exclusively or much higher (100 folds) expressed in pollen than other tissue types. Utilizing transcript abundance and correlation coefficient analysis, 1215 mature pollen-specific (MPS) genes and 1009 mature anther-specific (MAS) genes were identified in B73 transcriptome. These two gene sets had similar GO term and KEGG pathway enrichment patterns, indicating that their members share similar functions in the maize reproductive process. Of the genes, 623 were shared between the two sets, called mature anther- and pollen-specific (MAPS) genes, which represent the late-stage pollen-specific genes of the maize genome. Functional annotation analysis of MAPS showed that 447 MAPS genes (71.7% of MAPS) belonged to genes encoding pollen allergen protein. Their 2-kb promoters were analyzed for cis-element enrichment and six well-known pollen-specific cis-elements (AGAAA, TCCACCA, TGTGGTT, [TA]AAAG, AAATGA, and TTTCT) were found highly enriched in the promoters of MAPS. Interestingly, JA-responsive cis-element GCC box (GCCGCC) and ABA-responsive cis-element-coupling element1 (ABRE-CE1, CCACC) were also found enriched in the MAPS promoters, indicating that JA and ABA signaling likely regulate pollen-specific MAPS expression. This study describes a robust and straightforward pipeline to discover pollen-specific promotes from publicly available data while providing maize breeders and the maize industry a number of late-stage (mature) pollen-specific promoters for use in SPT for hybrid breeding and seed production.

THE QUALITY OF POLLEN GRAINS IN WHEAT MATURE ANTHERS OF ZHNITSA CULTIVAR IN PLANTA CONDITIONS

Biotechnological and selection investigations for making of wheat high-yielding resistant varieties require a significant amount of high-quality mature pollen. It is important to assess It is important to assess the quality of pollen grains in mature anthers in planta of the wheat genotypes included in the experiments. In the course of research the analysis of the histological status of mature anthers was carried out and qualitative cytological evaluation inside them pollen grain of spring soft wheat Zhnitsa cultivar was done in in planta conditions. It was shown that the structure of the wall locule anther presented by exothecium and endothecium is typical for cereals. It was established that 3-cell mature pollen grains are fertile (87-92%) and viable (75–80%) in general. At the same time in every mature anther abnormal pollen grains were observed and the cellular, nuclear, cytoplasmic and architectonic deviations from the norm were revealed. On the base of literature date the analysis of the reasons for the formation of abnormal pollen grains in planta was done and the classification of anomalies of plant pollen grains and the terminology used in this field of research were discussed.

Embriología de Erythroxylum havanense Jacq. (Erythroxylaceae)

We studied the development of reproductive structures in pin and thrum morphs of Erythroxylum havanense. The young anther wall consists of an epidermis, endothecium , 1-3 middle layers anda binucleate secretory tapetum. The mature anther wall has only two layers: epidermis and endothecium. Microspore tetrads are tetrahedral or isobilateral. Mature pollen grains are tricolporate, bicellular and contain starch grains. Exine sculpturing is verrugate in thrum pollen and reticulate in pin pollen. The ovule is sessile, pendulous, anatropous, bitegmic and crassinucellate. The embryo sac is heptacellular. An endothelium is differentiated. The endosperm development is nuclear, and the basal part of the nucellus persists during early endosperm development. Both integuments form the seed coat.

Pollen development and orbicule and pollen grain morphology in species of Cephalanthus (Rubiaceae-Naucleeae) from the Americas

This paper is the first embryological report on the genus Cephalanthus L. and contributes to future studies in other genera of the tribe Naucleeae. The development of the anther wall in Cephalanthus glabratus (Spreng.) K. Schum. corresponds to the dicot type and microsporogenesis is simultaneous. The young wall of the anther has four layers; epidermis, endothecium, one middle layer and the secretory tapetum. The tissue of the septum has idioblasts with crystalline sand. In the wall of the mature anther, only the endothecium and remnants of epidermal cells were preserved. The occurrence and morphology of orbicules were observed in the mature anthers of all three species of Cephalanthus with scanning electron microscopy. The orbicules have taxonomic value at species level, since these structures allow us to distinguish between the species analysed. The presence of a protruding oncus was observed for the first time in Cephalanthus in non-acetolysed pollen grains. According to our observations, this structure is not affected by the state of anther dehiscence in C. glabratus because the oncus is visible and prominent in the mature pollen grains in both indehiscent and dehiscent anthers.

Cytochemical and ultrastructural observations of anthers and pollen grains in Lathyrus undulatus Boiss

Cytochemical and ultrastructural observations of anthers and pollen grains inLathyrus undulatusBoissInLathyrus undulatusBoiss. (Fabaceae), the young microspore stage of anther development was characterized by the enlarged secretory tapetal cells, which presented an intense reaction with regard to protein, insoluble polysaccharides and lipids. At bicellular pollen stage, the middle layer and the tapetum degenerated. After degradation of the tapetum, epidermis and single row U-shaped endothecium existed in the mature anther wall, and pollen grains remained in the locus. Young microspores had a spherical and centrally located nucleus with one or two nucleoli, many spherical lipid bodies and starchy plastids. A mature pollen grain contains insoluble polysaccharides, proteins, lipids and calcium. The mature pollen had the following morphological characteristics: 3-zonocolporate, prolate, tectate (imperforate) type of exine and perforate type of structure. The intine formed an important constituent portion of the wall, and consisted two sublayers: an outer intine (exintine) and an inner intine (endintine). The well-defined exine was made up of lipoidal substances and protein, but the intine composed of insoluble polysaccharides and protein. The bicellular state of the pollen grains persisted to anthesis.

Microsporogenesis and microgametogenesis of Cardiospermum grandiflorum and Urvillea chacoensis (Sapindaceae, Paullinieae)

Microsporogenesis and microgametogenesis of two species, Cardiospermum grandiflorum Sw. and Urvillea chacoensis Hunz. (Sapindaceae, Paullinieae), were studied using light and transmission electron microscopy. Both species are monoecious, with staminate and hermaphrodite, although functionally pistillate, flowers. A comparative pollen-development study of these two floral morphs is reported. For the present study, five stages of pollen ontogeny were identified. The development of the anther wall is of basic type. Its wall consists of epidermis, endothecium, two middle layers and a uninucleate secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents the endothecium with well developed fibrillar thickenings, remains of tapetal cells, a single locule formed in the theca by dissolution of the septum before anther dehiscence and two-celled pollen grains when shed. In functionally pistillate flowers, the mature anthers present remnants of the middle layers, tapetal cells without signs of degradation, the theca with two locules and pollen grains uni- or bicellular, some of them with the cytoplasm collapsed. These anthers are not dehiscent. It can be concluded that male sterility is characterised by failure to produce functional pollen grains, an event that would be associated with the persistence of tapetal cells. Ultrastructural analysis clearly shows the difference in tapetal cells between the two flower morphs.

Anatomía y vascularización floral de Piriqueta racemosa, Turnera hassleriana y Turnera joelii (Turneraceae)

<span>The floral vascular anatomy of three species be10nging to two genera of Turneraceae is analyzed. The indumentum and the anatomical structure of peduncle, prophylls, perianth, nectaries, crown, androeciurn and gynoecium are described as well. The ovary is surrounded by a tube, the appendicular nature of which is confirmed: its basal portion is composed of calyx, corolla and staminal filaments, and its distal portion is formed only by the perianth. The expression "floral tube" is used to name this structure, following Takhtajan (1991). The nectaries are placed between the perianth and the stamens; in Piriqueta they are adnated to the floral tube while in Turnera they are located on the stamens. T. joelii seems to be more advanced because of the development of a nectar pocket. The crown is present only in Piriqueta, it has papillose epidermal cells and no vascular supply. Each episepalous stamen is supplied by one amphicribal bundle, which ends in the connective tissue. The wall of the mature anther is composed of epidermis and endothecium. Pollen grains are tricolporate and reticulate. The gynoecium has transmission tissue on the apical inner surface of the ovary (compitum), covering the placentae, ascending within the styles and appearing on the stigmas. The ovules are anatropous, bitegmic, crassinucelate, with zigzag micropyle.</span>

The role of initial cells in maize anther morphogenesis

The near absence of cell movement in plants makes clonal analysis a particularly informative method for reconstructing the early events of organ formation. We traced the patterns of cell division during maize anther development by inducing sector boundaries that preceded the earliest events of anther initiation. In doing this, we were able to estimate the smallest number of cells that are fated to form an anther, characteristic cell division patterns that occur during anther morphogenesis, and the relationship between the pre-existing symmetry of the initial cells and the final symmetry of the mature anther. Four general conclusions are made: (1) anthers are initiated from small groups of 12 or fewer cells in each of two floral meristematic layers; (2) the early growth of the anther is more like a shoot than a glume or leaf; (3) cell ancestry does not dictate basic structure and (4) the orientation of initial cells predicts the orientation of the four pollen-containing microsporangia, which define the axes of symmetry on the mature anther. The final point is discussed with other data, and an explanation involving a ‘structural template’ is invoked. The idea is that the orientation of initial cells within the floral meristem establishes an architectural pattern into which anther cells are recruited without regard to their cellular lineages. The structural template hypothesis may prove to be generally applicable to problems of pattern formation in plants.

Anther and pollen infection in relation to the pollen and seed transmissibility of two strains of barley stripe mosaic virus in barley

Anther and pollen infection in relation to seed and pollen transmission were studied for two different strains of barley stripe mosaic virus in 'Atlas' barley. Examination of sectioned anthers and pollen revealed that the seed- and pollen-transmitted isolate of the virus (MI-1) invaded the floral meristem of the host early and subsequently infected the pollen mother cells and sperms. During the premeiotic and meiotic stages of anther and pollen development, most virions of MI-1 were seen attached to microtubules, including those of the spindle. In later stages, the association of virions with microtubules diminished. Usually, MI-1 caused no apparent interference with normal mitosis and meiosis during development of anthers and pollen in central florets. Occasionally, however, the virus induced degeneration in anther and pollen-precursor cells before and during meiosis. By comparison, virions of the NSP strain, a strain which is not seed or pollen transmitted, could only be detected in wall cells of a single mature anther. None were discovered in the floral meristem or in pollen. It was also shown with unsectioned material that infection with either virus adversely affected anther and pollen development and that infection by MI-1 increased seed sterility.