Gaikwad, K. | bioRxiv Science

bioRxiv2020

Chromosome scale reference genome of Cluster bean (Cyamopsis tetragonoloba (L.) Taub.)

Clusterbean (Cyamopsis tetragonoloba (L.) Taub.), also known as Guar is a widely cultivated dryland legume of Western India and parts of Africa. Apart from being a vegetable crop, it is also an abundant source of a natural hetero-polysaccharide called guar gum or galactomannan which is widely used in cosmetics, pharmaceuticals, food processing, shale gas drilling etc. Here, for the first time we are reporting a chromosome-scale reference genome assembly of clusterbean, from a high galactomannan containing popular guar cultivar, RGC-936, by combining sequenced reads from Illumina, 10x Chromium and Oxford Nanopore technologies. The initial assembly of 1580 scaffolds with an N50 value of 7.12 Mbp was generated. Then, the final genome assembly was obtained by anchoring these scaffolds to a high density SNP map. Finally, a genome assembly of 550.31 Mbp was obtained in 7 pseudomolecules corresponding to 7 chromosomes with a very high N50 of 78.27 Mbp. We finally predicted 34,680 protein-coding genes in the guar genome. The high-quality chromosome-scale cluster bean genome assembly will facilitate understanding of the molecular basis of galactomannan biosynthesis and aid in genomics-assisted breeding of superior cultivars.

genomics↗

bioRxiv2020

Patterns of gene-body-methylation conservation and its divergent association with gene expression in Pigeonpea and Soybean

Pigeonpea and Soybean are closely related agronomically important legumes that diverged [~]23 million years ago followed by a whole genome duplication event in Soybean. However, the impact of divergence on their epigenomes is not known. Comparative epigenomics is a powerful tool to understand shaping of epigenomes and its functional consequences during evolution. In this study, we investigated the conservation and divergence of Gene body methylation (GbM) and gene-expression patterns between the two species. We compared their genome-wide DNA methylation landscape at single-base resolution and studied the influence of GbM on duplicate gene retention. Our results indicate that during the divergence of Pigeonpea and Soybean, the effects of methylation on gene expression evolved in a heterogeneous manner. GbM features-slow evolution rate and increased length remained conserved in Pigeonpea and Soybean. We also found that contrary to high CG-methylation conservation, non-CG methylated genes remained diverged during evolution due to transposons insertion in adjacent sequences. The methylation differences in paralogs were associated with expression divergence. Notably, we found that variably methylated marks are less likely to target evolutionary conserved sequences. Finally, our findings identify conservation of nitrogen-related genes during evolution, which are promising candidates for epi-alleles for crop improvement.

genomics↗