Search

We report the organization and transcription of diverged tandemly repeated Y-linked Su(Ste) genes that are considered as suppressors of testis-expressed X-linked-repeated Stellate genes that encode a protein sharing extensive homology with [Beta]-subunit of casein kinase 2. Clustering of restriction variants is confirmed. Size variants of Su(Ste) repeats appeared to be nonhomogeneously distributed among the P1 phage clones. Different ways of Su(Ste) RNA processing because of the appearance of new splice sites and polyadenylation signals were detected. The high extent of homology between Stellate and Su(Ste) repeats suggested a possibility of Stellate suppression by antisense transcription of Su(Ste) elements. The detection of only 'sense' Su(Ste) cDNAs in testis cDNA library, allows us to reject this proposal. The genomic and cDNA clones are shown to be equally diverged. This indicates widespread rather than restricted transcription capacity of these repeats.

Exine, the sporopollenin-based outer layer of the pollen wall, forms through an unusual mechanism involving interactions between two anther cell types: developing pollen and tapetum. How sporopollenin precursors and other components required for exine formation are delivered from tapetum to pollen and assemble on the pollen surface is still largely unclear. Here, we characterized an Arabidopsis (Arabidopsis thaliana) mutant, thin exine2 (tex2), which develops pollen with abnormally thin exine. The TEX2 gene (also known as REPRESSOR OF CYTOKININ DEFICIENCY1 (ROCK1)) encodes a putative nucleotide-sugar transporter localized to the endoplasmic reticulum. Tapetal expression of TEX2 is sufficient for proper exine development. Loss of TEX2 leads to the formation of abnormal primexine, lack of primary exine elements, and subsequent failure of sporopollenin to correctly assemble into exine structures. Using immunohistochemistry, we investigated the carbohydrate composition of the tex2 primexine and found it accumulates increased amounts of arabinogalactans. Tapetum in tex2 accumulates prominent metabolic inclusions which depend on the sporopollenin polyketide biosynthesis and transport and likely correspond to a sporopollenin-like material. Even though such inclusions have not been previously reported, we show mutations in one of the known sporopollenin biosynthesis genes, LAP5/PKSB, but not in its paralog LAP6/PKSA, also lead to accumulation of similar inclusions, suggesting separate roles for the two paralogs. Finally, we show tex2 tapetal inclusions, as well as synthetic lethality in the double mutants of TEX2 and other exine genes, could be used as reporters when investigating genetic relationships between genes involved in exine formation. [ABSTRACT FROM AUTHOR]

Pollen wall exine is usually deposited non-uniformly on the pollen surface, with areas of low exine deposition corresponding to pollen apertures. Little is known about how apertures form, with the novel Arabidopsis INP1 (INAPERTURATE POLLEN1) protein currently being the only identified aperture factor. In developing pollen, INP1 localizes to three plasma membrane domains and underlies formation of three apertures. Although INP1 homologs are found across angiosperms, they lack strong sequence conservation. Thus, it has been unclear whether they also act as aperture factors and whether their sequence divergence contributes to interspecies differences in aperture patterns. To explore the functional conservation of INP1 homologs, we used mutant analysis in maize and tested whether homologs from several other species could function in Arabidopsis. Our data suggest that the INP1 involvement in aperture formation is evolutionarily conserved, despite the significant divergence of INP1 sequences and aperture patterns, but that additional species-specific factors are likely to be required to guide INP1 and to provide information for aperture patterning. To determine the regions in INP1 necessary for its localization and function, we used fragment fusions, domain swaps, and interspecific protein chimeras. We demonstrate that the central portion of the protein is particularly important for mediating the species-specific functionality. [ABSTRACT FROM AUTHOR]

Pollen grains protect the sperm cells inside them with the help of the unique cell wall, the exine, which exhibits enormous morphological variation across plant taxa, assembling into intricate and diverse species-specific patterns. How this complex extracellular structure is faithfully deposited at precise sites and acquires precise shape within a species is not understood. Here, we describe the isolation and characterization of the novel Arabidopsis thaliana gene INAPERTURATE   POLLEN1 (INP1), which is specifically involved in formation of the pollen surface apertures, which arise by restriction of exine deposition at specific sites. Loss of INP1 leads to the loss of all three apertures in Arabidopsis pollen, and INP1 protein exhibits a unique tripartite localization in developing pollen, indicative of its direct involvement in specification of aperture positions. We also show that aperture length appears to be sensitive to INP1 dosage and INP1 misexpression can affect global exine patterning. Phenotypes of some inp1 mutants indicate that Arabidopsis apertures are initiated at three nonrandom positions around the pollen equator. The identification of INP1 opens up new avenues for studies of how formation of distinct cellular domains results in the production of different extracellular morphologies. [ABSTRACT FROM AUTHOR]

Sporopolleniri is the major component of the outer pollen wall (exine). Fatty acid derivatives and phenolics are thought to be its monomeric building blocks, but the precise structure, biosynthetic route, and genetics of sporopollenin are poorly understood. Based on a phenotypic mutant screen in Arabidopsis (Arabidopsis thaliana), we identified a cytochrome P450, designated CYP704B1, as being essential for exine development. CYP704B1 is expressed in the developing anthers. Mutations in CYP704B1. result in impaired pollen walls that lack a normal exine layer and exhibit a characteristic striped surface, termed zebra phenotype. Heterologous expression of CYP704B1 in yeast cells demonstrated that it catalyzes ω-hydroxylation of long-chain fatty acids, implicating these molecules in sporopollemn synthesis. Recently, an anther-specific cytochrome P450, denoted CYP703A2, that catalyzes in-chain hydroxylation of lauric acid was also shown to be involved in sporopollenin synthesis. This shows that different classes of hydroxylated fatty acids serve as essential compounds for sporopollenin formation. The genetic relationships between CYP704B1, CYP703A2, and another exirie gene, MALE STERJLITY2, which encodes a fatty acyl reductase, were explored. Mutations in all three genes resulted in pollen with remarkably similar zebra phenotypes, distinct from those of other known exine mutants. The double and triple mutant combinations did not result in the appearance of novel phenotypes or enhancement of single mutant phenotypes. This implies that each of the three genes is required to provide an indispensable subset of fatty acid-derived components within the sporopollenin biosynthesis framework. [ABSTRACT FROM AUTHOR]