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Date: Aug 24, 2020

BonnMu – a mutant collection for functional genetics in maize Researchers at the University of Bonn have developed the BonnMu resource, a collection of mutants in maize, which is now publicly available for functional genetic analyses. This study has been published in „Plant Physiology“.

Background and generation of new mutants in maize

The collection of mutants in maize (Zea mays), produced at the Institute of Crop Science and Resource Conservation of the University of Bonn, represents a library of induced mutations, developed by insertional mutagenesis. Insertional mutagenesis is a method, in which mutations are induced by random integration of mobile DNA fragments within the genome. If genes are hit by mobile DNA fragments their function is often impaired. Resulting mutations can have significant impact on different aspects of maize morphology, such as growth, photosynthesis (Figure 1), or fertility of the plants.

Dr. Caroline Marcon and coworkers of the Crop Functional Genomics group utilized Mutator (Mu)-Transposons, also known as jumping genes, to generate mutants in maize. On the campus Klein-Altendorf and in Endenich Mu-active maize lines were initially crossed into different American (B73 and Co125) and European (e.g., F7 and EP1) inbred lines. „This crossing was necessary, because only the Mu-active maize line expresses the enzyme transposase, which enables the immobile Mu-transposons of the inbred lines to move within their genome, thereby disrupting genes“, says Dr. Caroline Marcon, lead of the study. In the ongoing project more than 6.300 Mu-induced families of maize were produced so far. Successive analysis of those families by high-throughput sequencing identifies new Mu insertion sites and thus mutations. Collaborative researchers of the Crop Bioinformatics group, lead by Prof. Dr. Heiko Schoof, are significantly involved in the identification of novel insertion sites.

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Figure 1. A Mu-insertion (DNA-fragment in red, on the left) inside of a photosynthetic gene (DNA-fragment in green, on the left) could have an impact e.g., on the leaf color of young maize seedlings. The lacking chlorophyll in the leaves of mutated seedlings leads to their white appearance (albinism, left side of the photograph). In contrast, wild-type siblings still synthesize chlorophyll and have green leaves (right side of the photograph).

For the now published study, 1,152 transposon-induced maize families in the genetic background of B73 were sequenced, detecting about 41,000 germinal Mu-insertions that covered more than 16,300 (37%) of the annotated maize genes. In the study, Caroline Marcon and her colleagues compared for the first time all Mu-tagged genes of BonnMu with such genes of the American UniformMu resource. The UniformMu collection was generated in another genetic inbred background (W22). The comparison revealed that (1) insertion hotspots are conserved between the two genotypes B73 and W22, and that (2) the majority (75%) of the Mu-insertion sites are closer to the transcription start site than to the start codon of the affected genes. The latter was interesting insofar, because active genes are often characterized by open chromatin at the transcription start site. Chromatin describes the complex of DNA and protein making up the chromosomes. Relaxed chromatin could not only be easily accessible for the transcription machinery but also for the Mu-transposons. This assumption is now supported by the high number of Mu-insertion sites at the transcription start site, identified in the study.

For nearly 50% of all maize genes BonnMu insertional mutations exist already

Continous sequencing of the mutagenized maize families of the BonnMu project already identified more than 95,000 insertion sites, covering 21,613 (49%) of the 44,117 maize genes. „However, the aim of the project is, says project leader Caroline Marcon, to target as possible all genes of the maize genome by Mu-insertions. The mutant phenotypes will then help to explain the genes function. So far, only a few 100 genes are functionally chracterized in maize.“
The ongoing collaboration with researchers in the US enables regular incorporation of novel BonnMu insertion sites into the online database „MaizeGDB“ (maizegdb.org), representing one of the most important databases in maize research. On the web browser, BonnMu insertion sites in individual genes can be visualized (Figure 2) and seedling photographs of the mutagenized maize families are deposited (Figure 1). „Open access to „MaizeGDB“ enables interested researchers to specificially search for Mu-insertions which appear on their agenda. And upon request, we are providing the corresponding mutants for functional genetic analysis,“ says Caroline Marcon.

An exemplarily view into the „MaizeGDB“ database

Figure 2. An exemplarily view into the „MaizeGDB“ database (maizegdb.org) shows two BonnMu insertion sites in the gene with the accession number Zm00001d028826 (in blue). One of the insertions (BonnMu0021566) was detected in the mutagenized maize family BonnMu-4-A-1188.

Involved institutions and funding

International researchers of the Universities Florida and Missouri, and the U.S. Department of Agriculture contributed to that project. The project was financially supported by the Deutsche Forschungsgemeinschaft (DFG).

Publication

Marcon C, Altrogge L, et al., (2020) BonnMu: a sequence-indexed resource of transposon induced maize mutations for functional genomics studies, Plant Physiology, https://doi.org/10.1104/pp.20.00478.

Contact for the media

Dr. Caroline Marcon
BonnMu: Reverse genetic resources
INRES – Crop Functional Genomics
University of Bonn
Tel.: +49-(0) 0228-7354269
E-Mail: [Email protection active, please enable JavaScript.]
 

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