Symposium on transcriptional regulation in plants – University of Copenhagen

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Symposium on transcriptional regulation in plants with Frank Hochholdinger University of Bonn & Sascha Laubinger, University of Oldenburg

Frank Hochholdinger, INRES, Crop Functional Genomics, University of Bonn, Germany:
Single parent expression drives extensive complementation of non-syntenic genes in Zea mays L. hybrids

Distantly related maize inbred lines exhibit an exceptional degree of structural genomic diversity, which is probably unique among plants. Heterozygous F1-hybrid progeny of such inbred lines are often more vigorous than their homozygous parents, a phenomenon known as heterosis. Single-parent expression (SPE) is an extreme form of complementation on the gene expression level in hybrids.

SPE describes the observation that a gene is expressed in the hybrid but in only one of its two parental inbred lines. In previous work, we demonstrated that hybrids express more genes than their parental inbred lines as a consequence of SPE (Paschold et al., 2012). Moreover, we studied the plasticity of SPE in different root tissues of maize (Paschold et al., 2014) and in roots grown under drought stress (Marcon et al., 2017). These initial studies were performed in the inbred lines B73 and Mo17 and their reciprocal hybrids.

We now aim to extend and generalize our previous observations of transcriptomic patterns to a more diverse panel of maize inbred lines and their hybrid progeny and to different stages of maize root development. For this purpose we investigated how the genetic divergence of seven selected parental inbred lines (B73, Mo17, A554, H84, H99, Oh43, W64A) is reflected in the transcriptomic landscape of primary roots of their hybrid progeny during development.

A RNA-seq experiment was designed to maximize the number of direct comparisons among the parent-hybrid pairs and simultaneously to ensure a high degree of precision for indirect comparisons. For each developmental stage and each parent-hybrid combination we observed hundreds of SPE genes. Evolutionary aspects of these results and implications for hybrid vigor will be discussed.

Sascha Laubinger, University of Oldenburg, Germany:
Role of the splicing factor SERRATE in controling rapid stress-dependent activation of intron-less genes

Intron splicing increases proteome complexity, promotes RNA stability and export. Introns have also been shown to enhance transcription. However, the presence of introns, and the concomitant need for splicing, extends the time required for gene expression and can cause an undesirable delay in the activation of genes under stress conditions. Here, we show that the plant microRNA processing factor SERRATE (SE) plays an unexpected and pivotal role in the regulation of intronless genes.

Arabidopsis SE associated with more than 1000, mainly intronless, genes in a transcription-dependent manner. Chromatin-bound SE liaised with paused and elongating polymerase II complexes and promoted their association with intronless target genes. Our results indicate that stress-responsive genes are intron-poor, which negatively affects their expression strength, but that some genes circumvent this limitation via a novel SE-dependent transcriptional activation mechanism. Our finding that SE uncouples the trade-off between transcription strength and responsiveness makes SE a particularly interesting candidate for enhancing crop stress resistance.