Modern sugarcanes are polyploid interspecific hybrids, combining high sugar content from Saccharum officinarum with hardiness, disease resistance and ratooning of Saccharum spontaneum. Sequencing of a haploid S. spontaneum, AP85-441, facilitated the assembly of 32 pseudo-chromosomes comprising 8 homologous groups of 4 members each, bearing 35,525 genes with alleles defined. The reduction of basic chromosome number from 10 to 8 in S. spontaneum was caused by fissions of 2 ancestral chromosomes followed by translocations to 4 chromosomes. Surprisingly, 80% of nucleotide binding site-encoding genes associated with disease resistance are located in 4 rearranged chromosomes and 51% of those in rearranged regions. Resequencing of 64 S. spontaneum genomes identified balancing selection in rearranged regions, maintaining their diversity. Introgressed S. spontaneum chromosomes in modern sugarcanes are randomly distributed in AP85-441 genome, indicating random recombination among homologs in different S. spontaneum accessions. The allele-defined Saccharum genome offers new knowledge and resources to accelerate sugarcane improvement.
In the version of the article published, the author list is not accurate. Igor Cima and Min-Han Tan should have been authors, appearing after Mark Wong in the author list, while Paul Jongjoon Choi should not have been listed as an author. Igor Cima and Min-Han Tan both have the affiliation Institute of Bioengineering and Nanotechnology, Singapore, Singapore, and their contributions should have been noted in the Author Contributions section as "I.C. preprocessed Primary Cell Atlas data with inputs from M.-H.T. " The following description of the contribution of Paul Jongjoon Choi should not have appeared: "P.J.C. supported the smFISH experiments. " In the 'RCA: global panel' section of the Online Methods, the following sentence should have appeared as the second sentence, "An expression atlas of human primary cells (the Primary Cell Atlas) was preprocessed similarly to in ref. 55, " with new reference 55 (Cima, I. et al. Tumor-derived circulating endothelial cell clusters in colorectal cancer. Science Transl. Med. 8, 345ra89, 2016).
A phenol colour response test on the grain is used to identify varieties of wheat and rice. It is a harmful, damaging procedure due to the carcinogenic properties of phenol. The activity of polyphenol oxidase (PPO) provides the basis for the phenol colour reaction. The goal of this research was to assess a method similar to the phenol colour reaction, by determining where the polyphenol oxidase activity threshold lies for classifying rice types into different groups. The new PPO assay was applied to commercially available rice varieties with the intention of classifying those that ranged from extremely high to extremely low PPO levels into manageable categories. Substrates such as phenol, L-tyrosine, catechol and 3,4-dihydroxyphenylalanine (L-DOPA) were tested. Twenty cultivars cultivated under identical conditions were put through a screening using a standard assay [1.5 mL of 10 mM L-DOPA in 50 mM 3-(N-morpholino) propane sulphonic acid (MOPS) buffer, pH 6.5, with 3 to 5 seeds constantly rotated in a 2-mL microcentrifuge tube for 0.5 or 1 hour at room temperature]. At 30 minutes, PPO levels were assessed. Based on the PPO values, the varieties belonging to phenol colour groups such as black, dark brown, brown, light brown or no colour matched perfectly. Considering easiness in estimation and other advantages of PPO activity, L-DOPA is proposed as a means of identifying rice varieties instead of the phenol colour reaction test.
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