The genomic basis of the plant island syndrome in Darwin’s giant daisies

The repeated, rapid and often pronounced patterns of evolutionary divergence observed in insular plants, or the ‘plant island syndrome’, include changes in leaf phenotypes, growth, as well as the acquisition of a perennial lifestyle. Here, we sequence and describe the genome of the critically endangered, Galápagos-endemic species Scalesia atractyloides Arnot., obtaining a chromosome-resolved, 3.2-Gbp assembly containing 43,093 candidate gene models. Using a combination of fossil transposable elements, k-mer spectra analyses and orthologue assignment, we identify the two ancestral genomes, and date their divergence and the polyploidization event, concluding that the ancestor of all extant Scalesia species was an allotetraploid. There are a comparable number of genes and transposable elements across the two subgenomes, and while their synteny has been mostly conserved, we find multiple inversions that may have facilitated adaptation. We identify clear signatures of selection across genes associated with vascular development, growth, adaptation to salinity and flowering time, thus finding compelling evidence for a genomic basis of the island syndrome in one of Darwin’s giant daisies

Development of elite indica rice lines with wide spectrum of resistance to Thai blast isolates by pyramiding multiple resistance QTLs

The rice varieties IR64 and Jao Hom Nin (JHN) demonstrated a broad-spectrum resistance against the rice blast pathogens in Thailand. A genomic investigation unravelled many resistance genes residing on four genomic regions, chromosome 2 and 12 in IR64 and 1 and 11 in JHN. A cross between these varieties was made to combine resistance genes into a single genotype. Marker-assisted selection (MAS) was employed to identify F2 and F3 plants carrying a combination of four resistance QTLs in a homozygous fusion. Flanking markers RM212/RM319 and RM144/RM139 to blast resistant QTLs on chromosome 1 and 11 in JHN rice and tightly-linked markers RM208 and RM179 to blast resistant QTLs on chromosome 2 and 12 in IR64 rice variety were used for MAS. The stepwise MAS screening was brought in as a strategy to provide a cost-saving and minimum number of PCR performing to select resistant genotypes. F4 generation, lines carrying all resistant QTLs show a broader spectrum of resistance against 11 representatives of Thai blast pathogen isolates. (Résumé d'auteur