Prina, A. R. | bioRxiv Science

bioRxiv2021

Four large indels detected by cpTILLING in barley chloroplast mutator seedlings

In a previous work, a polymorphism detection strategy based on mismatch digestion was applied to the chloroplast genome of barley seedlings that carried the chloroplast mutator (cpm) genotype through many generations. Sixty-two different one- or two-nucleotide-polymorphisms were detected along with four large indels: an insertion of 15 bp in the intergenic region between tRNAHis and rps19 genes, a deletion of 620 bp in the psbA gene, a deletion of 79 bp in the intergenic region between rpl33 and rps18 genes and a deletion of 45 bp in the rps3 gene. In the present investigation, we analyzed direct repeats located at the borders of those four large indels. Furthermore, we investigated the consequences of protein expression of large indels located in coding regions. The deletion of 620 bp in the psbA gene was lethal at the second leaf stage when homoplastomic. The deletion of 45 bp in the rps3 gene, which eliminates 15 amino acids, did not affect the viability of the seedlings in homoplastomy. Interestingly, the deleted segment is also lacking in the wild type version of the rps3 gene of maize and sorghum. The presence of direct repeats at the borders of the four large indels suggests that they could have originated by illegitimate recombination. This would be in agreement with a previous hypothesis that the Cpm gene product would correspond to a mismatch repair (MMR) protein devoted to maintain plastome stability by playing fundamental roles in mismatch repair during replication and avoiding illegitimate recombination.

plant biology↗

bioRxiv2021

ATP-dependent Clp protease subunit C1, HvClpC1, is a strong candidate gene for barley variegation mutant luteostrians as revealed by genetic mapping and genomic re-sequencing

Implementation of next-generation sequencing in forward genetic screens greatly accelerated gene discovery in species with larger genomes, including many crop plants. In barley, extensive mutant collections are available, however, the causative mutations for many of the genes remains largely unknown. Here we demonstrate how a combination of low-resolution genetic mapping, whole-genome resequencing and comparative functional analyses provides a promising path towards candidate identification of genes involved in plastid biology and / or photosynthesis, even if genes are located in recombination poor regions of the genome. As a proof of concept, we simulated the prediction of a candidate gene for the recently cloned variegation mutant albostrians (HvAST / HvCMF7) and adopted the approach for suggesting HvClpC1 as candidate gene for the yellow-green variegation mutant luteostrians. Author SummaryForward genetics is an approach of identifying a causal gene for a mutant phenotype and has proven to be a powerful tool for dissecting the genetic control of biological processes in many species. A large number of barley mutants was generated in the 1940s to 1970s when mutation breeding programs flourished. Genetic dissection of the causative mutations responsible for the phenotype, however, lagged far behind, limited by lack of molecular markers and high-throughput genotyping platforms. Next-generation sequencing technologies have revolutionized genomics, facilitating the process of identifying mutations underlying a phenotype of interest. Multiple mapping-by-sequencing or cloning-by-sequencing strategies were established towards fast gene discovery. In this study, we used mapping-by-sequencing to identify candidate genes within coarsely delimited genetic intervals, for two variegation mutants in barley - luteostrians and albostrians. After testing the approach using the example of the previously cloned albostrians gene HvAST, the gene HvClpC1 could be delimited as candidate gene for luteostrians. The mapping-by-sequencing strategy implemented here is generally suited for surveying barley mutant collections for phenotypes affecting fundamental processes of plant morphology, physiology and development.

genetics↗