The classical Ubisch bodies carry a sporophytically produced structural protein (RAFTIN) that is essential for pollen development

National Research Council Canada, Ottawa, Ontario, Canada
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 12/2003; 100(24):14487-92. DOI: 10.1073/pnas.2231254100
Source: PubMed


Pollen fecundity is crucial to crop productivity and also to biodiversity in general. Pollen development is supported by the tapetum, a metabolically active sporophytic nurse layer that devotes itself to this process. The tapetum in cereals and a vast majority of other plants is of the nonamoeboid type. Unable to reach out to microspores, it secretes nutrients into the anther locule where the microspores reside and develop. Orbicules (Ubisch bodies), studied in various plants since their discovery approximately 140 years ago, are a hallmark of the secretory tapetum. Their significance to tapetal or pollen development has not been established. We have identified in wheat and rice an anther-specific single-copy gene (per haploid genome equivalent) whose suppression in rice by RNA interference nearly eliminated the seed set. The flowers in the transgenics were normal for female functions, but the pollen collapsed and became less viable. Further characterization of the gene product, named RAFTIN, in wheat has shown that it is present in pro-orbicule bodies and it is accumulated in Ubisch bodies. Furthermore, it is targeted to microspore exine. Although the carboxyl portion of RAFTINs shares short, dispersed amino acid sequences (BURP domain) in common with a variety of proteins of disparate biological contexts, the occurrence RAFTIN per se is limited to cereals; neither the Arabidopsis genome nor the vast collection of ESTs suggests any obvious dicot homologs. Furthermore, our results show that RAFTIN is essential for the late phase of pollen development in cereals.

Download full-text


Available from: Raju Datla
  • Source
    • "Sporopollenin composition, structure and biosynthesis appear conserved among all land plants. Phylogenetic and genomic analysis support this as putative orthologs of ACOS5, PKSA, PKSB, CYP703A2 and CYP704B1 are present in flowering plants, but absent from green algae (Wang et al. 2003;de Azevedo Souza et al. 2009;Kim et al. 2010;Wallace et al. 2011;Yang et al. 2014). Supporting this hypothesis, Physcomitrella patens encodes for an enzyme with in vitro preference for hydroxyl fatty acyl-CoA esters that is capable of hydroxyalkylpyrone synthase activity, suggesting that PpASCL is a functional ortholog of Arabidopsis PKSA and that the pathway to sporopollenin is conserved in land plants (Colpitts et al. 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Pollen development is a critical step in plant development that is needed for successful breeding and seed formation. Manipulation of male fertility has proved a useful trait for hybrid breeding and increased crop yield. However although there is a good understandingdeveloping of the molecular mechanisms of anther and pollen anther development in model species, such as Arabidopsis and rice, little is known about the equivalent processes in important crops. Nevertheless the onsetof increased genomic information and genetic tools is facilitating translation of information from the models to crops, such as barley and wheat; this will enable increased understanding and manipulation of these pathways for agricultural improvement. This article is protected by copyright. All rights reserved.
    Preview · Article · Aug 2015 · Journal of Integrative Plant Biology
  • Source
    • "autofluorescent ORBs were ob - served in acos5 , pksa pksb , tkpr1 , and their respective double mutants in the abcg26 background by 2 - P microscopy ( Figures 2 and 3 ; Supplemental Figure 5 ) . These had obvious similarity to the orbicules observed in the locules of some species in asso - ciation with exine deposition ( Huysmans et al . , 1998 ; Wang et al . , 2003 ) . The presence of ORBs in the absence of polyketide biosynthesis suggested the existence of a second pathway that requires the polyketide component of sporopollenin in order to be assembled into the exine and that these metabolites are exported into the locule independently of ABCG26 ."
    [Show abstract] [Hide abstract]
    ABSTRACT: Pollen grains are encased by a multilayered, multifunctional wall. The sporopollenin and pollen coat constituents of the outer pollen wall (exine) are contributed by surrounding sporophytic tapetal cells. Because the biosynthesis and development of the exine occurs in the innermost cell layers of the anther, direct observations of this process are difficult. The objective of this study was to investigate the transport and assembly of exine components from tapetal cells to microspores in the intact anthers of Arabidopsis thaliana. Intrinsically fluorescent components of developing tapetum and microspores were imaged in intact, live anthers using two-photon microscopy. Mutants of ABCG26, which encodes an ATP binding cassette transporter required for exine formation, accumulated large fluorescent vacuoles in tapetal cells, with corresponding loss of fluorescence on microspores. These vacuolar inclusions were not observed in tapetal cells of double mutants of abcg26 and genes encoding the proposed sporopollenin polyketide biosynthetic metabolon (ACYL COENZYME A SYNTHETASE5, POLYKETIDE SYNTHASE A [PKSA], PKSB, and TETRAKETIDE a-PYRONE REDUCTASE1), providing a genetic link between transport by ABCG26 and polyketide biosynthesis. Genetic analysis also showed that hydroxycinnamoyl spermidines, known components of the pollen coat, were exported from tapeta prior to programmed cell death in the absence of polyketides, raising the possibility that they are incorporated into the exine prior to pollen coat deposition. We propose a model where ABCG26-exported polyketides traffic from tapetal cells to form the sporopollenin backbone, in coordination with the trafficking of additional constituents, prior to tapetum programmed cell death.
    Full-text · Article · Nov 2014 · The Plant Cell
  • Source
    • "A number of BURP genes have been identified. In addition to those genes that were sporadically isolated in special tissues, developmental stages or conditions [4], [5], [6], [7], [8], 5 members in Arabidopsis thaliana [9], 17 in Oryza sativa L. [10], 23 in Glycine max [11], 15 in Zea mays, 11 in Sorghum vulgare [12] and 18 in Populus trichocarpa [13] were identified genome-widely. The expression of these genes exhibits different temporal and spatial profiles [7], [10], and some of them can be regulated by various stress treatments [10], [11], [14], suggesting that BURP genes might play diverse roles in plant development and stress responses. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The plant-specific BURP family proteins play diverse roles in plant development and stress responses, but the function mechanism of these proteins is still poorly understood. Proteins in this family are characterized by a highly conserved BURP domain with four conserved Cys-His repeats and two other Cys, indicating that these proteins potentially interacts with metal ions. In this paper, an immobilized metal affinity chromatography (IMAC) assay showed that the soybean BURP protein SALI3-2 could bind soft transition metal ions (Cd2+, Co2+, Ni2+, Zn2+ and Cu2+) but not hard metal ions (Ca2+ and Mg2+) in vitro. A subcellular localization analysis by confocal laser scanning microscopy revealed that the SALI3-2-GFP fusion protein was localized to the vacuoles. Physiological indexes assay showed that Sali3-2-transgenic Arabidopsis thaliana seedlings were more tolerant to Cu2+ or Cd2+ stresses than the wild type. An inductively coupled plasma optical emission spectrometry (ICP-OES) analysis illustrated that, compared to the wild type seedlings the Sali3-2-transgenic seedlings accumulated more cadmium or copper in the roots but less in the upper ground tissues when the seedlings were exposed to excessive CuCl2 or CdCl2 stress. Therefore, our findings suggest that the SALI3-2 protein may confer cadmium (Cd2+) and copper (Cu2+) tolerance to plants by helping plants to sequester Cd2+ or Cu2+ in the root and reduce the amount of heavy metals transported to the shoots.
    Full-text · Article · Jun 2014 · PLoS ONE
Show more