Abstract
Pepper (Capsicum annuum L.) is an economically important vegetable crop worldwide. Although many genes associated with anther and pollen development have been identified, little is known about the mechanism of pollen abortion in pepper. Here, we identified and isolated two putative aborted microspore (AMS) isoforms from pepper flowers: CaAMS1 and CaAMS2. Sequence analysis showed that CaAMS2 was generated by retention of the fourth intron in CaAMS1 pre-mRNA. CaAMS1 encodes a putative protein with a basic helix-loop-helix (bHLH) domain belonging to the MYC subfamily of bHLH transcription factors, and it is localized to the nucleus. Truncated CaAMS2-1 and CaAMS2-2 are produced by alternative splicing. Quantitative real-time PCR analysis showed that CaAMS (referred to CaAMS1 and CaAMS2-2) was preferentially expressed in stamens and its expression level gradually decreases with flower development. RNA in situ hybridization analysis showed that CaAMS is strongly expressed in the tapetum at the tetrad and uninucleate stages. Downregulation of CaAMS led to partial shortened filaments, shriveled, indehiscent stamens and abortive pollens in pepper flowers. Several genes involved in pollen exine formation were downregulated in defective CaAMS-silenced anthers. Thus, CaAMS seems to play an important role in pepper tapetum and pollen development by regulating a complex genetic network.
Highlights
Anther and pollen development play a crucial role in the life cycle of flowering plants
We isolated two putative aborted microspore (AMS) isoforms from pepper flower buds, designated as CaAMS1 (Accession No MH230199) and CaAMS2
We found that CaAMS2 was generated by retention of the fourth intron (Accession No MH230200) in CaAMS1 pre-mRNA
Summary
Anther and pollen development play a crucial role in the life cycle of flowering plants. TPD1 encodes a small secreted protein that possibly works in coordination with the EMS1/EXS gene product to determine tapetal cells fate in A. thaliana [15]. Other genes involved in late tapetum development or function in A. thaliana were reported These included DYSFUNCTIONAL TAPETUM 1 (DYT1), MALE STERILITY 1/2 (MS1/2), ABORTED MICROSPORE (AMS), and AtMYB103. DYT1 encodes a putative helix-loop-helix (bHLH) transcription factor and plays a crucial role in tapetal differentiation and early function [17]. AMS encodes a bHLH transcription factor and plays a crucial role in tapetum development and post-meiotic microspore development [18]. Several genes involved in pollen exine formation were significantly downregulated in defective CaAMS-silenced anthers Overall, these traits indicate that CaAMS plays an important role in pepper tapetal and pollen development by means of a complex genetic network. CaAMS seems to be a practical and effective tool to artificially regulate stamens’ fertility and further improve the efficiency of breeding practices
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