bims-plasge 2019-03-24 papers

Nat Genet. 2019 Mar 18.

Gossypium barbadense and Gossypium hirsutum genomes provide insights into the origin and evolution of allotetraploid cotton.

Allotetraploid cotton is an economically important natural-fiber-producing crop worldwide. After polyploidization, Gossypium hirsutum L. evolved to produce a higher fiber yield and to better survive harsh environments than Gossypium barbadense, which produces superior-quality fibers. The global genetic and molecular bases for these interspecies divergences were unknown. Here we report high-quality de novo-assembled genomes for these two cultivated allotetraploid species with pronounced improvement in repetitive-DNA-enriched centromeric regions. Whole-genome comparative analyses revealed that species-specific alterations in gene expression, structural variations and expanded gene families were responsible for speciation and the evolutionary history of these species. These findings help to elucidate the evolution of cotton genomes and their domestication history. The information generated not only should enable breeders to improve fiber quality and resilience to ever-changing environmental conditions but also can be translated to other crops for better understanding of their domestication history and use in improvement.

DOI: https://doi.org/10.1038/s41588-019-0371-5

Plant Reprod. 2019 Mar 21.

Transgenerational effects of inter-ploidy cross direction on reproduction and F2 seed development of Arabidopsis thaliana F1 hybrid triploids.

Dorota Duszynska, Bjarni Vilhjalmsson, Rosa Castillo Bravo, Sandesh Swamidatta, Thomas E Juenger, Mark T A Donoghue, Aurélie Comte, Magnus Nordborg, Timothy F Sharbel, Galina Brychkova, Peter C McKeown, Charles Spillane.

KEY MESSAGE: Reproduction in triploid plants is important for understanding polyploid population dynamics. We show that genetically identical reciprocal F1 hybrid triploids can display transgenerational epigenetic effects on viable F2 seed development. The success or failure of reproductive outcomes from intra-species crosses between plants of different ploidy levels is an important factor in flowering plant evolution and crop breeding. However, the effects of inter-ploidy cross directions on F1 hybrid offspring fitness are poorly understood. In Arabidopsis thaliana, hybridization between diploid and tetraploid plants can produce viable F1 triploid plants. When selfed, such F1 triploid plants act as aneuploid gamete production "machines" where the vast majority of gametes generated are aneuploid which, following sexual reproduction, can generate aneuploid swarms of F2 progeny (Henry et al. 2009). There is potential for some aneuploids to cause gametophyte abortion and/or F2 seed abortion (Henry et al. 2009). In this study, we analyse the reproductive success of 178 self-fertilized inter-accession F1 hybrid triploids and demonstrate that the proportions of aborted or normally developed F2 seeds from the selfed F1 triploids depend upon a combination of natural variation and cross direction, with strong interaction between these factors. Single-seed ploidy analysis indicates that the embryonic DNA content of phenotypically normal F2 seeds is highly variable and that these DNA content distributions are also affected by genotype and cross direction. Notably, genetically identical reciprocal F1 hybrid triploids display grandparent-of-origin effects on F2 seed set, and hence on the ability to tolerate aneuploidy in F2 seed. There are differences between reciprocal F1 hybrid triploids regarding the proportions of normal and aborted F2 seeds generated, and also for the DNA content averages and distributions of the F2 seeds. To identify genetic variation for tolerance of aneuploidy in F2 seeds, we carried out a GWAS which identified two SNPs, termed MOT and POT, which represent candidate loci for genetic control of the proportion of normal F2 seeds obtained from selfed F1 triploids. Parental and grandparental effects on F2 seeds obtained from selfed F1 triploids can have transgenerational consequences for asymmetric gene flow, emergence of novel genotypes in polyploid populations, and for control of F2 seed set in triploid crops.

Keywords: Epigenetic; F1 hybrid; Plant evolution; Reproduction; Transgenerational effect; Triploid bridge

DOI: https://doi.org/10.1007/s00497-019-00369-6

Mol Plant. 2019 Mar 16. pii: S1674-2052(19)30094-2. [Epub ahead of print]

Molecular mechanism of protein import specificity to chloroplasts and mitochondria in plant cells.

Dong Wook Lee, Sumin Lee, Junho Lee, Seungjin Woo, Md Abdur Razzak, Alessandro Vitale, Inhwan Hwang.

Plants possess both types of endosymbiotic organelles, chloroplasts and mitochondria. Transit peptides and presequences function as signal sequences for specific import into chloroplasts and mitochondria, respectively. However, how these highly similar signal sequences confer this import specificity remains elusive. Here, we show that mitochondrial- or chloroplast-specific import involves two distinct steps, specificity determination and translocation across envelopes, which are mediated by the N-terminal regions and functionally interchangeable C-terminal regions, respectively, of transit peptides and presequences. The domain harboring multiple-arginine and hydrophobic sequence motifs was identified in the N-terminal regions of presequences as the mitochondrial specificity factor. The presence of this domain or the absence of arginine residues in the N-terminal regions of otherwise common targeting signals confers specificity for mitochondria or chloroplasts, respectively. AtToc159, an import receptor of chloroplast also contributes to determining chloroplast import specificity. We propose that common ancestral sequences were functionalized into mitochondrial- and chloroplast-specific signal sequences by the presence and absence, respectively, of multiple-arginine and hydrophobic sequence motifs in the N-terminal regions.

Keywords: C-terminal common translocation domain; Import specificity determination; N-terminal specificity domain; Presequence; Protein import into chloroplasts and mitochondria; Transit peptide

DOI: https://doi.org/10.1016/j.molp.2019.03.003