Unique Changes in Mitochondrial Genomes Associated with Reversions of S-Type Cytoplasmic Male Sterility in Maizemar

Cytoplasmic male sterility (CMS) in plants is usually associated with the expression of specific chimeric regions within rearranged mitochondrial genomes. Maize CMS-S plants express high amounts of a 1.6-kb mitochondrial RNA during microspore maturation, which is associated with the observed pollen abortion. This transcript carries two chimeric open reading frames, orf355 and orf77, both unique to CMS-S. CMS-S mitochondria also contain free linear DNA plasmids bearing terminal inverted repeats (TIRs). These TIRs recombine with TIR-homologous sequences that precede orf355/orf77 within the main mitochondrial genome to produce linear ends. Transcription of the 1.6-kb RNA is initiated from a promoter within the TIRs only when they are at linear ends. Reversions of CMS-S to fertility occur in certain nuclear backgrounds and are usually associated with loss of the S plasmids and/or the sterility-associated region. We describe an unusual set of independently recovered revertants from a single maternal lineage that retain both the S plasmids and an intact orf355/orf77 region but which do not produce the 1.6-kb RNA. A 7.3-kb inversion resulting from illegitmate recombination between 14-bp microrepeats has separated the genomic TIR sequences from the CMS-associated region. Although RNAs containing orf355/orf77 can still be detected in the revertants, they are not highly expressed during pollen development and they are no longer initiated from the TIR promoter at a protein-stabilized linear end. They appear instead to be co-transcribed with cytochrome oxidase subunit 2. The 7.3-kb inversion was not detected in CMS-S or in other fertile revertants. Therefore, this inversion appears to be a de novo mutation that has continued to sort out within a single maternal lineage, giving rise to fertile progeny in successive generations

Circular and linear mitochondrial genomes in cytoplasmic male sterile maize [abstract]

Abstract only availableCytoplasmic male sterility (CMS) is a maternally inherited condition in which a plant has an inability to produce viable pollen. It is usually due to the production of a toxic chimeric protein within the mitochondria during the maturation of pollen grains. In maize (Zea mays), there are three types of CMS: CMS-T, CMS-C and CMS-S. The S-type of cytoplasmic male sterility (CMS-S) in maize is associated with the expression of a rearranged mitochondrial DNA region. This CMS-S-specific region includes two co-transcribed chimeric open reading frames, orf355 and orf77. The nuclear restorer-of-fertility gene, Rf3, cleaves all transcripts containing both orfs, including the CMS-S-specific linear 1.6 kb mRNA; this results in male fertility. The Lancaster Surecrop-derived inbred line A619 carries a different and weaker restorer called Rf9. Fertility restoration by Rf3 and Rf9 was compared for their effects upon the CMS-associated region of mitochondrial DNA. Unlike Rf3, Rf9 affects the organization of the CMS-S-specific region. It appears to do this by affecting recombination between linear "S" plasmids and the CMS-S-specific region of the main mitochondrial genome, which produces a linear end from which transcripts for the 1.6 kb mRNA are initiated. By reducing the amount of recombination, Rf9 reduces the amount of linear template available for transcribing the S-associated 1.6 kb RNA. A reduction in this transcript is associated with an increase in pollen survival. We have studied the effects of the two restorer-of-fertility genes from several different inbred lines on the amounts of integrated and linearized orf355/orf77 genes within CMS-S mtDNA.MU Monsanto Undergraduate Research Fellowshi

Kanamycin resistance during in vitro development of pollen from transgenic tomato plants

Effects of kanamycin on pollen germination and tube growth of pollen from non-transformed plants and from transgenic tomato plants containing a chimaeric kanamycin resistance gene were determined. Germination of pollen was not affected by the addition of kanamycin to the medium in both genotypes. Kanamycin, however, severely affected tube growth of pollen from non-transformed plants, while pollen from plants containing the chimaeric gene were less sensitive and produced significantly longer tubes at kanamycin concentrations between 200-400 mg l-1. Apparently, this resistance for kanamycin correlates with the expression of the chimaeric gene during male gametophytic development.

Study of temperature and moisture content in wood aircraft wings in different climates

This report is one of a series issued in cooperation with the Army-Navy-Civil Committee on Aircraft Design Criteria under the supervision of the Aeronautical Board

Analysis of the Maize dicer-like1 Mutant, fuzzy tassel, Implicates MicroRNAs in Anther Maturation and Dehiscence

Sexual reproduction in plants requires development of haploid gametophytes from somatic tissues. Pollen is the male gametophyte and develops within the stamen; defects in the somatic tissues of the stamen and in the male gametophyte itself can result in male sterility. The maize fuzzy tassel (fzt) mutant has a mutation in dicer-like1 (dcl1), which encodes a key enzyme required for microRNA (miRNA) biogenesis. Many miRNAs are reduced in fzt, and fzt mutants exhibit a broad range of developmental defects, including male sterility. To gain further insight into the roles of miRNAs in maize stamen development, we conducted a detailed analysis of the male sterility defects in fzt mutants. Early development was normal in fzt mutant anthers, however fzt anthers arrested in late stages of anther maturation and did not dehisce. A minority of locules in fzt anthers also exhibited anther wall defects. At maturity, very little pollen in fzt anthers was viable or able to germinate. Normal pollen is tricellular at maturity; pollen from fzt anthers included a mixture of unicellular, bicellular, and tricellular pollen. Pollen from normal anthers is loaded with starch before dehiscence, however pollen from fzt anthers failed to accumulate starch. Our results indicate an absolute requirement for miRNAs in the final stages of anther and pollen maturation in maize. Anther wall defects also suggest that miRNAs have key roles earlier in anther development. We discuss candidate miRNAs and pathways that might underlie fzt anther defects, and also note that male sterility in fzt resembles water deficit-induced male sterility, highlighting a possible link between development and stress responses in plants.ECU Open Access Publishing Support Fun

Hierarchical selection theory and sex ratios I. General solutions for structured populations

Models of sex-ratio evolution in structured populations are derived withG. R. Price's covariance form for the hierarchical analysis of natural selection (1970, Nature 227, 520-521). Previous work on competition among related males for mates (local mate competition), competition among related females for a limiting resource (local resource competition), inbreeding, group selection, and asymmetry of genetic inheritance between males and females, are subsumed under a general formulation for sex-ratio biases in structured populations. I found that the evolutionarily stable strategy sex ratio (males:females) for diploids is 1 - [varrho]m:1 - [varrho]f, where [varrho]m is the regression coefficient of relatedness of the controlling genotypes on males competing for mates, [varrho]f is the regression of controlling genotypes on females that compete for a fixed, limiting resource, and there is no inbreeding. For inbreeding and no competition among females, the evolutionarily stable strategy is 1 - [varrho]m:1 + [varrho]mf, where [varrho]mf is the regression of controlling genotypes on females' mates.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26154/1/0000231.pd