No abstract

The xenia effect refers to the phenomenon whereby the pollen genotype directly affects seed and fruit development during the period from fertilization to seed germination, which leads to different characteristics in phenotypic traits. The xenia effect can create differences in the endosperm and embryo formed after double fertilization and can also alter various fruit parameters, such as the fruit-ripening period; the fruit shape, size, and color; the flavor quality, such as sugars and acids; as well as the nutrient quality, such as anthocyanins. The xenia effect manifests in various ways, playing an important role in increasing the yield of fruit trees, improving fruit appearance and internal quality, as well as in directional breeding. Compared with other pomology research areas, our understanding of the xenia effect is still in its infancy. Currently, xenia is classified into two types: xenia and metaxenia. In the former, the direct effects of the pollen genotype are exhibited in the syngamous parts of the ovules; that is, the embryo and endosperm only. In the latter, the effects of the pollen genotype are demonstrated in structures other than the embryo and endosperm; that is, in tissues derived wholly from the mother plant material, in seed parts such as the nucellus and testa, as well as in the carpels and accessory tissues. However, the current classification has various shortcomings. In the present study, we propose a novel classification based on whether the appearance of xenia results from the tissue formed by double fertilization. Three xenia types are proposed: double-fertilization xenia, non–double-fertilization xenia, and combined xenia. The new classification has great theoretical and practical significance for future studies on the xenia effect and its mechanisms and also provides a more effective, broader application of xenia in improving the yield and quality of fruit trees.

MicroRNAs (miRNAs) related to phytohormone signal transduction and self-incompatibility may play an important role in the xenia effect. However, associated research in this area is still lacking in rabbiteye blueberry (Vaccinium ashei). In this study, we identified miRNAs, predicted their target genes, performed functional enrichment analysis of the target genes, and screened for miRNAs related to phytohormone signaling and self-incompatibility. A total of 491 miRNAs were identified, of which 27 and 67 known miRNAs as well as 274 and 416 new miRNAs were found in the rabbiteye blueberry cultivars Brightwell and Premier, respectively. Compared with ‘Premier’, 31 miRNAs were upregulated and 62 miRNAs were downregulated in ‘Brightwell’. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis indicated that the 4985 target genes predicted were involved in biosynthesis of amino acids, plant–pathogen interaction, and spliceosome pathways. A total of 10, one, one, five, two, five, and two candidate miRNAs related to auxin, cytokinin, gibberellin, abscisic acid, ethylene, brassinosteroid, and salicylic acid signaling, respectively, in rabbiteye blueberry pollen were identified. Further analysis indicated that novel_miR_49 was a candidate miRNA related to self-incompatibility, and their target gene was maker-VaccDscaff21-snap-gene-21.37. In addition, the KEGG enrichment analysis of the target genes of novel_miR_49 showed that they were involved in the ribosome, aminoacyl-tRNA biosynthesis, and glycosylphosphatidylinositol-anchor biosynthesis pathways. The results revealed that the microRNAs of rabbiteye blueberry pollen regulated to phytohormone signal transduction and self-incompatibility signal transduction based on related to auxin, cytokinin, gibberellin, abscisic acid, ethylene, brassinosteroid, and salicylic acid signaling. Results suggest that more research of the effects of miRNAs on regulation of hormone signal transduction and self-incompatibility is necessary for elucidating the molecular mechanism of the xenia effect.

Pinus massoniana L. is an important andi typical ectomycorrhizal dependent tree species in Guizhou. In order to reveal the community structure and driving factors for ectomycorrhizal fungi (ECMF) of P. massoniana in Karst region, Illumina MiSeq high-throughput sequencing was used to study the diversities and community structure characteristics of ECMF in the rhizosphere soil of P. massoniana L. in the three sites of Xugongdian (SY1), Dishuiguanyin (SY2) and Yingtaowan (SY3) in Yuntai Mountain, Guizhou. The ectomycorrhizal fungi belonged to 2 phyla, 5 classes, 11 orders, and 38 genera. At the phylum level, ectomycorrhizal fungi mainly belonged to the Basidiomycota, accounting for 96.20% of all ectomycorrhizal fungi; the rest were Ascomycota fungi, accounting for only 3.8%. At the genus level, Russula, Cortinarius, Suillus, Inocybe, Tricholoma, Tomentella, Sebacina, Scleroderma, Cenococcum were the dominant ectomycorrhizal fungi of P. massoniana . The diversity and richness of ectomycorrhizal fungi communities in the three sites were significantly different. The ectomycorrhizal fungal community structures in SY1 and SY3 were similar, but were quite different from those in SY2. All soil factors explained 97.7% of the differences in the community composition of ECMF, with AP, TN, OM and AK being the main driving factors for the differences in the community composition of ectomycorrhizal fungi in the three sites. Bangladesh J. Bot. 51(4): 913-922, 2022 (December) Special