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Microspore embryogenesis is a model for developmental plasticity and cell fate decisions. To investigate the role of miRNAs in this development, we sequenced sRNAs and the degradome of barley microspores collected prior to (day 0) and after (days 2 and 5) the application of a stress treatment known to induce embryogenesis. Microspores isolated at these timepoints were uniform in both appearance and in their complements of sRNAs. We detected 68 miRNAs in microspores. The abundance of 51 of these miRNAs differed significantly during microspore development. One group of miRNAs was induced when the stress treatment was applied, prior to being repressed when microspores transitioned to embryogenesis. Another group of miRNAs were up-regulated in day-2 microspores and their abundance remained stable or increased in day-5 microspores, a timepoint at which the first clear indications of the transition toward embryogenesis were visible. Collectively, these miRNAs might play a role in the modulation of the stress response, the repression of gametic development, and/or the gain of embryogenic potential. A degradome analysis allowed us to validate the role of miRNAs in regulating 41 specific transcripts. We showed that the transition of microspores toward the embryogenesis pathway involves miRNA-directed regulation of members of the ARF, SPL, GRF, and HD-ZIPIII transcription factor families. We noted that 41.5% of these targets were shared between day-2 and day-5 microspores while 26.8% were unique to day-5 microspores. The former set may act to disrupt transcripts involved in pollen development while the latter set may drive the commitment to embryogenesis.

In barley, it is possible to induce embryogenesis in the haploid and uninucleate microspore to obtain a diploid plant that is perfectly homozygous. To change developmental fates in this fashion, microspores need to engage in cellular de-differentiation, interrupting the pollen formation, and restore totipotency prior to engaging in embryogenesis. In this work, we used the barley cultivar Gobernadora to characterize the transcriptome of microspores prior to (day 0) and immediately after (days 2 and 5) the application of a stress pretreatment. A deep RNA-seq analysis revealed that microspores at these three time points exhibit a transcriptome of ∼14k genes, ∼90% of which were shared. An expression analysis identified a total of 3,382 differentially expressed genes (DEGs); of these, 2,155 and 2,281 DEGs were respectively identified when contrasting expression at days 0 and 2 and at days 2 and 5. These define 8 expression profiles in which DEGs share a common up- or down-regulation at these time points. Up-regulation of numerous glutathione S-transferase and heat shock protein genes as well as down-regulation of ribosomal subunit protein genes was observed between days 0 and 2. The transition from microspores to developing embryos (days 2 vs. 5) was marked by the induction of transcription factor genes known to play important roles in early embryogenesis, numerous genes involved in hormone biosynthesis and plant hormonal signal transduction in addition to genes involved in secondary metabolism. This work sheds light on transcriptional changes accompanying an important developmental shift and provides candidate biomarkers for embryogenesis in barley.

The aim of this study was to measure genetic diversity and population structure among 92 Canadian barley cultivars using two types of molecular markers (SSRs and DArTs) and pedigree data. A total of 368 alleles were identified at 50 SSR loci. The number of alleles per locus ranged between 2 and 13 ([bar.x]= 7.36) and PIC values ranged from 0.34 to 0.86 ([bar.x] = 0.69). For the biallelic DArT markers, the genetic distance matrix was based on 971 markers whose PIC values ranged between 0.06 and 0.50 ([bar.x] = 0.39). A third distance matrix was computed based on the kinship coefficient. Clustering of genotypes was performed based on the genetic distance matrix and the three dendrograms obtained showed the genetic relationships among barley cultivars. The topological similarity of the three dendrograms was estimated using a congruence index and showed the three dendrograms to be in very good agreement. Statistical analysis also showed a highly significant correlation between the SSR and DArT matrices (r = 0.80, p < 0.002) compared with lower yet significant correlations of the pedigree data with both marker types (r = 0.46, p < 0.002; r = 0.52, p < 0.002). Finally, we assessed linkage disequilibrium in this germplasm and found it to be quite extensive, as the mean distance between marker pairs with significant (P < 0.001) [r.sup.2] values > 0.5 was 3.8 cM. Information obtained from comparing results of different genetic diversity estimation methods should be useful for the improvement and conservation of barley genetic resources. Key words: barley, genetic distance, kinship coefficient, linkage disequilibrium (LD), SSR, DArT. L'objectif de cette etude etait de mesurer la diversite genetique et la structure des populations parmi 92 cultivars canadiens d'orge en utilisant deux types de marqueurs moleculaires (SSR et DArT) et le pedigree. Un total de 368 alleles ont ete identifies a 50 locus SSR. Le nombre d'alleles par locus variait de 2 a 13 ([bar.x] = 7,36) et l'indice PIC variait entre 0,34 et 0,86 ([bar.x] = 0,69). Pour les marqueurs bialleliques DArT, la matrice de distance genetique s'est basee sur 971 marqueurs dont les indices PIC variaient entre 0,06 et 0,50 ([bar.x] = 0,39). Une troisieme matrice de distance a ete calculee basee sur le coefficient de parente. Un groupement des genotypes a ete effectue base sur les matrices de distances genetiques et les trois dendrogrammes obtenus ont montre les relations genetiques entre les cultivars d'orge. La similarite topologique des trois dendrogrammes a ete estimee en utilisant un indice de congruence et a montre que les trois dendrogrammes presentent une tres bonne concordance. Les analyses statistiques ont egalement montre une correlation tres significative entre les matrices SSR et DArT (r = 0,80, p < 0,002) mais une faible correlation positive entre la matrice basee sur le pedigree et les matrices basees sur les deux types de marqueurs (r = 0,46, p < 0,002; r = 0,52, p < 0,002). Finalement, nous avons etudie le desequilibre de liaison (LD) au sein de cette collection et avons trouve qu'elle s'etendait sur une bonne distance; en effet, la distance genetique entre marqueurs presentant un LD significatif (P < 0,001) et des valeurs de [r.sup.2] > 0,5 etait de 3,8 cM en moyenne. L'information obtenue en comparant les resultats de differentes methodes d'estimation de la diversite genetique sera utile pour l'amelioration et la conservation des ressources genetiques chez l'orge. Mots-cles: orge, distance genetique, coefficient de parente, desequilibre de liaison (LD), SSR, DArT., Introduction Barley (Hordeum vulgare L.) is one of the oldest cultivated crops in the world (Morrell and Clegg 2007). Today, it constitutes the fourth most cultivated cereal in the world [...]

Andrew D. Evans, Anthropology at War: World War I and the Science of Race in Germany. Chicago: University of Chicago Press, 2010, 312 pp. Sometimes it takes a modest, carefully-focused [...]