In Vitro Amphidiploid Induction of A Distant Hybrid Populus Simonii × P. Euphratica Cv. ‘Xiaohuyang-2’ and its Effect on Plant Morphology and Anatomy

In plants, highly gametic sterility of distant hybrids usually restricts their utilization in breeding programs. Amphidiploid induction produced by somatic chromosome doubling of distant hybrids can effectively restore their gametic fertility. In this study, nodal-segment and leaf explants of a distant hybrid Populus simonii × P. euphratica cv. ‘Xiaohuyang-2’ were used to induce chromosome doubling with colchicine in vitro. Although chromosome doubling of the nodal-segment explants only produced mixoploids, the treatments of leaf explants on adventitious bud regeneration medium successfully produced 4 amphidiploids, which might be attributed to the direct organogenesis of the adventitious buds on the leaf explants. The highest amphidiploid induction frequency was 16.7%. Both the explant survival rate and polyploidization frequency were significantly affected by colchicine concentration and exposure time. The amphidiploid plants were significantly differed from the diploid and mixoploid plants on morphological and anatomical characteristics. They had larger, thicker, and greener leaves than the diploids and mixoploids. The changes of stomatal features also accompanied with increase of ploidy level. The induced amphidiploid plants of the distant hybrid ‘Xiaohuyang-2’ are expected to play important roles in breeding programs of Populus in future, which can be used as a bridge parent with ability of unreduced gamete formation to cross with fast-growth germplasms to produce triploids pyramiding desirable traits of fast growth, easy cutting propagation, and salt and drought tolerances.

Arbuscular Mycorrhizal Fungi Regulate MAPK Pathway Genes Expression and Enhance Drought Tolerance of Populus Simonii × P. Nigra Seedlings

Background: Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with host plants, which can promote plants to absorb more water and nutrients, and thus improve the stress resistance of plants. Our study aimed to investigate the effects of Rhizophagus irregularis on Populus simonii × P. nigra seedlings under drought stress. Results: The experiment was a completely random design with two water conditions (well-watered or drought stress) and two AMF treatments (inoculated with or without R. irregularis). Our results showed that mycorrhizal seedlings performed less oxidative damage and stronger tolerance of drought, which recorded higher photosynthesis and less concentrations of Malondialdehyde (MDA), H2O2, and proline under drought stress versus non-mycorrhizal seedlings. Under drought stress, AMF inoculation reduced soluble sugar concentration in leaves but promoted its accumulation in roots. The superoxide dismutase (SOD) activity in leaves and roots, and catalase (CAT) activity in roots of mycorrhizal seedlings were lower than non-mycorrhizal seedlings, but CAT activity in leaves of mycorrhizal seedlings was higher than non-mycorrhizal seedlings under drought stress. Drought stress and AMF inoculation both induced the expressions of MAPKs of P. simonii × P. nigra, but the expression patterns of MAPKs under four treatments were obviously different.Conclusions: Overall, our results demonstrated that mycorrhizal seedlings had less oxidative damage and stronger tolerance to drought. MAPKs expressions of P. simonii×P. nigra (PsnMAPKs) were induced by drought stress and AMF inoculation, and the expression patterns of PsnMAPKs in response to drought stress were different between mycorrhizal and non-mycorrhizal seedlings. Non-mycorrhizal seedlings may be adapted to drought by up-regulating MAPKs expressions leading to stomatal closure. Drought stress decreased serval PsnMAPKs expressions induced by AMF inoculation, which may be associated with mycorrhizal colonization.

Leaf Size Development Differences and Comparative Trancriptome Analyses of Two Poplar Genotypes

The plant leaf, the main organ of photosynthesis, is an important regulator of growth. To explore the difference between leaf size of Populusdeltoides ‘Danhong’ (Pd) and Populus simonii ‘Tongliao1’ (Ps), we investigated the leaf length, leaf width, leaf thickness, leaf area, leaf mass per area (LMA), and cell size of leaves from two genotypes and profiled the transcriptome-wide gene expression patterns through RNA sequencing. Our results show that the leaf area of Pd was significantly larger than that of Ps, but the epidermal cell area was significantly smaller than that of Ps. The difference of leaf size was caused by cell numbers. Transcriptome analysis also revealed that genes related to chromosome replication and DNA repair were highly expressed in Pd, while genes such as the EXPANSIN (EXPA) family which promoted cell expansion were highly expressed in Ps. Further, we revealed that the growth-regulating factors (GRFs) played a key role in the difference of leaf size between two genotypes through regulation of cell proliferation. These data provide a valuable resource for understanding the leaf development of the Populus genus.

Genome-wide identification and expression analysis of the xyloglucan endotransglucosylase/hydrolase gene family in poplar

Background Xyloglucan endotransglucosylase/hydrolase (XTH) family plays an important role in cell wall reconstruction and stress resistance in plants. However, the detailed characteristics of XTH family genes and their expression pattern under salt stress have not been reported in poplar. Results In this study, a total of 43 PtrXTH genes were identified from Populus simonii × Populus nigra, and most of them contain two conserved structures (Glyco_hydro_16 and XET_C domain). The promoters of the PtrXTH genes contain mutiple cis-acting elements related to growth and development and stress responses. Collinearity analysis revealed that the XTH genes from poplar has an evolutionary relationship with other six species, including Eucalyptus robusta, Solanum lycopersicum, Glycine max, Arabidopsis, Zea mays and Oryza sativa. Based on RNA-Seq analysis, the PtrXTH genes have different expression patterns in the roots, stems and leaves, and many of them are highly expressed in the roots. In addition, there are11 differentially expressed PtrXTH genes in the roots, 9 in the stems, and 7 in the leaves under salt stress. In addition, the accuracy of RNA-Seq results was verified by RT-qPCR. Conclusion All the results indicated that XTH family genes may play an important role in tissue specificity and salt stress response. This study will lay a theoretical foundation for further study on molecular function of XTH genes in poplar.

Вплив урбоекосистем на фітонцидну активність деревних рослин

Мета дослідження – виявлення зв'язку та просте-ження закономірності між фітонцидною активністюдеревних рослин і вмістом зелених пігментів у їхніхлистках в урбанізованому середовищі. Методи. Комплексне використання польового, лабо-раторного, математично-статистичного, розрахунко-во-порівняльного методів і системного аналізу.Результати. Дуже висока антимікробна дія булавиявлена в листків A. platanoides, P. simonii та S. vulgarisщодо обох тест-культур на всіх моніторингових точкаху серпні. Для всіх видів характерний літній тип фітон-цидності. У досліджених видів виявлено тенденцію добільшої антимікробної активності щодо грам-негативноїбактерії E. coli порівняно з B. subtilis, окрім листків P. xcanadensis. На всіх ділянках, навіть у контролі, вмістхлорофілу а перевищував уміст хлорофілу b (табл. 2).На частку хлорофілу а припадає 50–56% від загальноїмаси зелених пігментів на забрудненій ділянці.Співвідношення хлорофілу a до хлорофілу b ( а/b)у нормально розвинутому фотосинтетичному апаратістановить 2,5–3. Навесні цей показник був нижчим занорму на всіх ділянках, влітку відбулося його збіль-шення, що можна пояснити ростом листків та форму-ванням фотосинтетичного апарату. На моніторинговійточці І влітку показник а/b був нижчим за норму в усіхвидів, окрім T. cordata.Висновки. Проведено аналіз фітонцидної актив-ності деревних культур в умовах урбанізованого сере-довища. Виявлено високу фітонцидну активність Acerplatanoides, Populus simonii та Syringa vulgaris у серпні.Встановлено специфічність антимікробної дії дерев-них рослин щодо Bacillus subtilis та Esherichia coli. Назабрудненій ділянці вздовж автомагістралі спостеріга-лося зниження суми хлорофілів порівняно з контролемта зростання фітонцидної активності. Вміст хлорофілуа на І дослідній ділянці в усіх досліджених рослин,окрім Tilia cordata, перевищив уміст хлорофілу b. Длябільшості видів характерна висока антимікробна актив-ність протягом досліджуваного періоду, крім Robiniapseudoacacia та Tilia cordata.

Molecular Karyotyping on Populus simonii × P. nigra and the Derived Doubled Haploid

The molecular karyotype could represent the basic genetic make-up in a cell nucleus of an organism or species. A doubled haploid (DH) is a genotype formed from the chromosome doubling of haploid cells. In the present study, molecular karyotype analysis of the poplar hybrid Populus simonii × P. nigra (P. xiaohei) and the derived doubled haploids was carried out with labeled telomeres, rDNA, and two newly repetitive sequences as probes by fluorescence in situ hybridization (FISH). The tandem repeats, pPC349_XHY and pPD284_XHY, with high-sequence homology were used, and the results showed that they presented the colocalized distribution signal in chromosomes. For P. xiaohei, pPD284_XHY produced hybridizations in chromosomes 1, 5, 8, and 9 in the hybrid. The combination of pPD284_XHY, 45S rDNA, and 5S rDNA distinctly distinguished six pairs of chromosomes, and the three pairs of chromosomes showed a significant difference in the hybridization between homologous chromosomes. The repeat probes used produced similar FISH hybridizations in the DH; nevertheless, pPD284_XHY generated an additional hybridization site in the telomere region of chromosome 14. Moreover, two pairs of chromosomes showed differential hybridization distributions between homologous chromosomes. Comparisons of the distinguished chromosomes between hybrid and DH poplar showed that three pairs of chromosomes in the DH presented hybridization patterns that varied from those of the hybrid. The No. 8 chromosome in DH and one of the homologous chromosomes in P. xiaohei shared highly similar FISH patterns, which suggested the possibility of intact or mostly partial transfer of the chromosome between the hybrid and DH. Our study will contribute to understanding the genetic mechanism of chromosomal variation in P. xiaohei and derived DH plants.

СТАН ПРЕДСТАВНИКІВ РОДУ POPULUS L. У ПАРКУ «САКСАГАНСЬКИЙ» МІСТА КРИВИЙ РІГ (ДНІПРОПЕТРОВСЬКА ОБЛАСТЬ)

We studied the state of poplars in the park Saksaganskyi in Kryvyi Rih, their share being 14.6 % of the total number of trees and 21 % of the total number of taxa. The vast majority of specimens are aged 40; such trees in the conditions of Kryvyi Rih need constant care. The general condition of poplars can be considered weakened, it may be due to the lack of proper care. Plantations of Populus simonii are of the best state, while those of P. berolinensis are of the worst state. Preliminary expert assessment of the peculiarities of poplar operation, in particular the determination of the optimal pruning type and age limits for complete removal of plants, is appropriate to determine maintenance works. It is recommended to enrich the park plantings with new plantings of P. bolleana, which have high aesthetic properties, as well as to introduce species of this genus, in particular P. suaveolens Fisch. ex Loudon, P. balsamifera L. et al.

Genome-wide Identification and Expression Analysis of the Eyloglucan Endotransglucosylase/hydrolase Gene Family in Poplar

Background: Xyloglucan endotransglucosylase/hydrolase (XTH) plays an important role in the process of plant cell wall reconstruction, and also involved in plants stress resistance. However, its characteristics of XTH family genes have not been reported in poplar. Results: In this study, we found 43 PtrXTH genes from Populus simonii × Populus nigra, and most of them contain two conserved structures (Glyco_hydro_16 and XET_C domain). The promoter regions of the PtrXTH genes contain many cis-acting elements related to growth and development and adverse stresses responses. Collinearity analysis revealed that the XTH family from poplarhave an evolutionary relationship with other five species, including Eucalyptus robusta, Solanum lycopersicum, Glycine max, Arabidopsis, Zea mays and Oryza sativa. Through RNA-Seq analysis, we found that the PtrXTH genes have different expression patterns in the roots, stems and leaves, and many of them are highly expressed in the roots. In addition, we found 11 differentially expressed PtrXTH genes in the roots, 9 in the stems, and 7 in the leaves under salt stress, and verified the accuracy of RNA-Seq analysis by RT-qPCR.Conclusion: All the results indicated that XTH family genes may play an important role in tissue specificity and salt stress response. This study laid a theoretical foundation for further study on the functions of XTH genes in poplar.