In tetraploid wheat, both non-brittle spike and free-threshing are labour-saving traits that increase the efficiency of post-harvest processing, which could have been an incentive for rapid domestication of the Near Eastern cereals, thus refuting the recently proposed hypothesis regarding extra labour associated with the domesticated phenotype (non-brittle spike) and its presumed role in extending the domestication episode time frame.
Grafting is an important, widely used plant propagation technique but its physiological effects are as yet insufficiently understood. Recent studies indicate that movement of proteins and small RNAs through the graft union might be involved. MicroRNAs are known to play a significant role in regulation of higher plants’ developmental and metabolic traits. Extending this logic, we hypothesize that changes in activity of specific microRNAs are one of the mechanisms involved in physiological effects of grafting. The objective of the present study was to test this hypothesis. We determined the expression of a broad range of microRNAs in Citrus leaf petioles, as affected by grafting. Four stock/scion combinations (‘Merav’ mandarin and ‘Star Ruby‘ grapefruit scions X ‘Troyer’ citrange and ‘Volkamer’ lemon rootstocks), rootstock auto-grafts and plants of the variety used as rootstock (= non-grafted) were examined. Grafting caused a dramatic reduction in the expression of the major microRNAs, miR156 (and miR157), which appear to be associated with reduction of juvenility in perennial woody plants. This effect was strongest in hetero-grafts but evident also in auto-grafts. Expression of miR894 also declined upon grafting. Differences in the expression of miR397 were found among grafted scion cultivars, while in non-grafted rootstocks expression of miR397 was barely detectable. Bioinformatic analysis confirmed the presence of miR397 in the citrus genome, validated its sequence and demonstrated its ability to form a stem loop. The differences in miR397 expression might be related to specific copper and other micronutrient requirements of citrus stock-scion combinations.Thus, our results support the hypothesis, indicating the involvement of specific microRNAs in engendering physiological effects of grafting in Citrus. The precise, underlying mechanism needs to be elucidated.
BackgroundWheat domestication is considered as one of the most important events in the development of human civilization. Wheat spikelets have undergone significant changes during evolution under domestication, resulting in soft glumes and larger kernels that are released easily upon threshing. Our main goal was to explore changes in transcriptome expression in glumes that accompanied wheat evolution under domestication.MethodsA total of six tetraploid wheat accessions were selected for transcriptome profiling based on their rachis brittleness and glumes toughness. RNA pools from glumes of the central spikelet at heading time were used to construct cDNA libraries for sequencing. The trimmed reads from each library were separately aligned to the reference sub-genomes A and B, which were extracted from wheat survey sequence. Differentially expression analysis and functional annotation were performed between wild and domesticated wheat, to identity candidate genes associated with evolution under domestication. Selected candidate genes were validated using real time PCR.ResultsTranscriptome profiles of wild emmer wheat, wheat landraces, and wheat cultivars were compared using next generation sequencing (RNA-seq). We have found a total of 194,893 transcripts, of which 73,150 were shared between wild, landraces, and cultivars. From 781 differentially expressed genes (DEGs), 336 were down-regulated and 445 were up-regulated in the domesticated compared to wild wheat genotypes. Gene Ontology (GO) annotation assigned 293 DEGs (37.5 %) to GO term groups, of which 134 (17.1 %) were down-regulated and 159 (20.4 %) up-regulated in the domesticated wheat. Some of the down-regulated DEGs in domesticated wheat are related to the biosynthetic pathways that eventually define the mechanical strength of the glumes, such as cell wall, lignin, pectin and wax biosynthesis. The reduction in gene expression of such genes, may explain the softness of the glumes in the domesticated forms. In addition, we have identified genes involved in nutrient remobilization that may affect grain size and other agronomic traits evolved under domestication.ConclusionsThe comparison of RNA-seq profiles between glumes of wheat groups differing in glumes toughness and rachis brittleness revealed a few DEGs that may be involved in glumes toughness and nutrient remobilization. These genes may be involved in processes of wheat improvement under domestication.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1996-0) contains supplementary material, which is available to authorized users.
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