MicroRNA expression changes following synthesis of three full-sib Populus triploid populations with different heterozygosities

Identification and Functional Prediction of CircRNAs in Leaves of F1 Hybrid Poplars with Different Growth Potential and Their Parents

Circular RNAs (CircRNAs) regulate plant growth and development; however, their role in poplar heterosis is unclear. We identified 3722 circRNAs in poplar leaves, most of which were intergenic (57.2%) and exonic (40.2%). The expression of circRNAs in F1 hybrids with high growth potential was higher than that in those with low growth potential. Non-additive expression of circRNAs and single-parent expression of circRNAs (SPE-circRNAs) might regulate poplar heterosis through microRNA sponging and protein translation, respectively. DECs among F1 hybrids with different growth potentials might regulate the growth potential of poplar via microRNA sponging. Correlation analysis between circRNA expression and its parent gene expression showed that SPE-M circRNA (circRNAs expressed by male parent only) might regulate poplar heterosis by inhibiting parent gene expression, while other circRNAs might regulate poplar heterosis by enhancing parent gene expression. Weighted correlation network analysis of gene/circRNA expression showed that circRNAs mainly regulate poplar heterosis via carbohydrate metabolism, amino acid metabolism, energy metabolism, and material transport. In addition, we identified seven circRNAs that positively or negatively regulate poplar heterosis. Thus, non-additively expressed circRNAs and SPE circRNAs are involved in regulating poplar heterosis, and DECs among F1 hybrids with different growth potentials were involved in regulating poplar growth potential.

Breeding polyploid Populus: progress and perspective

Populus is a genus of 25-30 species of deciduous flowering plants in the family Salicaceae, which are primarily planted in short-rotation planations for producing timber, pulpwood, wooden products as well as bioenergy feedstock; they are also widely planted in agricultural fields and along roadsides as shelter forest belts for windbreak, decoration, and reduction of pollutants and noise. Moreover, their fast-growth and good adaptation to marginal lands enable them to provide some critical ecosystem services at various phytoremediation sites for land restoration and reclaimation. Thanks to their important roles, breeding for fast growing poplar trees has been one of the most important objectives for nearly a century. One of the most demonstrated, documented achievements in this aspect is polyploid breeding, especially triploid breeding. This paper critically reviews the various techniques used in inducing triploid plants, including natural 2n formation, artificial induction of 2n male and female gemmates through chemical or physical treatments, trait characterization of the triploid and tetraploid breeding populations, unveiling the molecular mechanisms underpinning the significantly improved traits, and identification and selection of the best triploid progenies. This review also recapitulated the challenges and strategies facing the future of triploid breeding in Populus, including amelioration of 2n gamete induction techniques and efficiency, selection of the best parents and identification of the best progrenies, utilization of the huge amount of genomic, transcriptomic, proteomic, metabolomic, and other omics data for selecting parents for improving target traits.

Integrated analysis of mRNA-seq and miRNA-seq reveals the advantage of polyploid Solidago canadensis in sexual reproduction

BACKGROUND

The invasion of Solidago canadensis probably related to polyploidy, which may promotes its potential of sexual reproductive. S. canadensis as an invasive species which rapidly widespread through yield huge numbers of seed, but the mechanism remains unknown. To better understand the advantages of sexual reproduction in hexaploid S. canadensis, transcriptome and small RNA sequencing of diploid and hexaploid cytotypes in flower bud and fruit development stages were performed in this study.

RESULTS

The transcriptome analysis showed that in the flower bud stage, 29 DEGs were MADS-box related genes with 14 up-regulated and 15 down-regulated in hexaploid S. canadensis; 12 SPL genes were detected differentially expressed with 5 up-regulated and 7 down-regulated. In the fruit development stage, 26 MADS-box related genes with 20 up-regulated and 6 down-regulated in hexaploid S. canadensis; 5 SPL genes were all up-regulated; 28 seed storage protein related genes with 18 were up-regulated and 10 down-regulated. The weighted gene co-expression network analysis (WGCNA) identified 19 modules which consisted of co-expressed DEGs with functions such as sexual reproduction, secondary metabolism and transcription factors. Furthermore, we discovered 326 miRNAs with 67 known miRNAs and 259 novel miRNAs. Some of miRNAs, such as miR156, miR156a and miR156f, which target the sexual reproduction related genes.

CONCLUSION

Our study provides a global view of the advantages of sexual reproduction in hexaploid S. canadensis based on the molecular mechanisms, which may promote hexaploid S. canadensis owing higher yield and fruit quality in the process of sexual reproduction and higher germination rate of seeds, and finally conductive to diffusion, faster propagation process and enhanced invasiveness.

Molecular Mechanism of Vegetative Growth Advantage in Allotriploid Populus

Allotriploid poplar has a prominent vegetative growth advantage that impacts dramatically on lumber yield. The growth regulation is complex which involves abundant genes, metabolic and signaling pathways, while the information about the functional control process is very little. We used high-throughput sequencing and physiological index measurement to obtain a global overview of differences between allotriploid and diploid Populus. The genes related to plant growth advantage show a higher expression compared to diploid, and most of them are revolved around hormones, photosynthesis and product accumulation. Thus, allotriploid Populus showed more efficient photosynthesis, carbon fixation, sucrose and starch synthesis, and metabolism as well as augmented biosynthesis of auxin, cytokinin, and gibberellin. These data enable the connection of metabolic processes, signaling pathways, and specific gene activity, which will underpin the development of network models to elucidate the process of triploid Populus advantage growth.