RESUMEN
In nonplant species, many heat-shock transcription factors (HSFs) undergo spatiotemporal-specific alternative splicing. However, little is known about the spatiotemporal-specific splicing of HSFs in plants. Previously, we reported that the alfalfa HSF gene MsHSF1 undergoes multiple alternative splicing events in various tissues. Here, we identified another spliced transcript isoform, MsHSF1c, containing a 177-base tandem repeat, and showed that the low-abundance MsHSF1c is a nodule-specific transcript of MsHSF1. We also found that MsHSF1 presents multiple alleles with single-base variations and the expression of MsHSF1 alleles has allele-specific differences in alfalfa nodules. Because single-base variations at position 1006 change the AT of MsHSF1b to GT in MsHSF1b-3, creating a pair of donor/acceptor sites with the AG of MsHSF1b/1b-1 at position 827-828 for pre-mRNA splicing, we suggest that MsHSF1c may be generated by trans-splicing between alleles MsHSF1b-3 and MsHSF1b or MsHSF1b-1. These results provide new insight into the role of tissue-specific contribution in the transcription of plant HSF genes.
Asunto(s)
Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica de las Plantas , Proteínas de Choque Térmico/genética , Medicago sativa/genética , Proteínas de Plantas/genética , Trans-Empalme , Factores de Transcripción/genética , Transcripción Genética , Alelos , Secuencia de Aminoácidos , Secuencia de Bases , Variación Genética , Factores de Transcripción del Choque Térmico , Datos de Secuencia Molecular , Isoformas de Proteínas/genética , Análisis de Secuencia de ADN , Secuencias Repetidas en TándemRESUMEN
Plant heat shock transcription factors (HSF) are highly complex. In this study, we identified an alfalfa HSF gene MsHSF1 that is composed of four exons and three introns in the encoding region. The intron1-exon2-intron2-exon3-intron3 as an intervening sequence was inserted at the conserved position that separates the coding region for the DNA-binding domain by single intron in other known plant HSF genes. Alternative splicing of MsHSF1 has generated five transcript isoforms. Spliced transcript MsHSF1b consisted of exon1 and exon4, encodes a class A1 HSF protein that can specifically bind to the heat shock elements in vitro. Other four spliced transcripts (MsHSF1a-1 to 4) consist of exon1, part of the intervening sequence and exon4. These transcripts carry the premature termination codon and are low-abundant. Apparently these transcripts are the targets of nonsense-mediated mRNA decay (NMD). These results provide new insight into roles in the expression regulation of plant HSF genes.
Asunto(s)
Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica de las Plantas/genética , Proteínas de Choque Térmico/genética , Medicago sativa/genética , Proteínas de Plantas/genética , Sitios de Empalme de ARN/genética , Factores de Transcripción/genética , Secuencia de Bases , Factores de Transcripción del Choque Térmico , Datos de Secuencia MolecularRESUMEN
Several studies have demonstrated that the Rhizobium nifA gene is an activator of nitrogen fixation acting in nodule bacteria. To understand the effects of the Sinorhizobium meliloti nifA gene on Alfalfa, the cDNA-AFLP technique was employed to study the changes in gene expression in nifA mutant nodules. Among the approximately 3,000 transcript-derived fragments, 37 had differential expression levels. These expression levels were subsequently confirmed by reverse Northern blot and RT-polymerase chain reaction. Sequence analyses revealed that 21 cDNA fragments corresponded to genes involved in signal communication, protein degradation, nutrient metabolism, cell growth and development.