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The Arabidopsis ABORTED MICROSPORES (AMS) gene encodes a MYC class transcription factor
Anna-Marie Sorensen1, Sandra Kröber, Ulrike S Unte
1Department of Molecular Plant Genetics, Max Planck Institute for Plant Breeding Research, Cologne, Germany. sorensen@mpiz-koeln.mpg.de
Abstract:
Visual screening of a T-DNA mutagenised population of Arabidopsis thaliana for an absence of silique elongation lead to the isolation of the aborted microspores (ams) mutant that shows a sporophytic recessive male sterile phenotype. Homozygous mutant plants are completely devoid of mature pollen. Pollen degeneration occurs shortly after release of the microspores from the tetrad, prior to pollen mitosis I. Premature tapetum and microspore degeneration are the primary defects caused by this lesion, while a secondary effect is visualised in the stamen filaments, which are reduced in length and lie beneath the receptive stigma at flower opening. The disrupted gene was isolated and revealed a T-DNA element to be inserted into the eighth exon of a basic helix-loop-helix (bHLH) gene located on chromosome II. This protein sequence contains a basic DNA binding domain and two alpha helices separated by a loop, typical of a transcription factor belonging to the MYC sub family of bHLH genes. Therefore, AMS plays a crucial role in tapetal cell development and the post-meiotic transcriptional regulation of microspore development within the developing anther.
Insights
The aborted microspores (ams) mutant in Arabidopsis thaliana exhibits male sterility due to premature pollen and tapetum degeneration. This research identifies a bHLH gene crucial for microspore development and anther function.
Area of Science:
- Plant genetics
- Molecular biology
- Developmental biology
Background:
- Male sterility in plants can arise from various genetic defects affecting pollen development.
- The tapetum plays a critical role in nourishing microspores and ensuring pollen viability.
Purpose of the Study:
- To identify and characterize genes involved in microspore and tapetal development in Arabidopsis thaliana.
- To understand the molecular basis of sporophytic male sterility.
Main Methods:
- Screening of a T-DNA mutagenized Arabidopsis population for male sterile phenotypes.
- Genetic analysis to determine the inheritance pattern of the mutation.
- Gene isolation and characterization through T-DNA insertion mapping.
- Analysis of pollen and tapetal development using microscopy.
Main Results:
- Isolation of the aborted microspores (ams) mutant with a recessive sporophytic male sterile phenotype.
- Homozygous ams mutants are devoid of mature pollen, with degeneration occurring post-meiosis but pre-mitosis I.
- Primary defects include premature tapetum and microspore degeneration, with secondary effects on stamen filament length.
- The mutation results from a T-DNA insertion in a basic helix-loop-helix (bHLH) gene on chromosome II.
Conclusions:
- The AMS gene, a MYC-type bHLH transcription factor, is essential for tapetal cell development and post-meiotic microspore development.
- Disruption of AMS leads to male sterility through impaired anther development.
- This study highlights the critical role of bHLH transcription factors in plant reproductive development.