Molecular Mechanisms of the miR396b-GRF1 Module Underlying Rooting Regulation in Acer rubrum L.

Rooting and root development in Acer rubrum have important effects on overall growth. A. rubrum does not take root easily in natural conditions. In this study, the mechanisms of the miR396b-GRF1 module underlying rooting regulation in A. rubrum were studied. The subcellular localization and transcriptional activation of miR396b and its target gene growth regulating factor 1 (GRF1) were investigated. These experiments showed that GRF1 was localized in the nucleus and had transcriptional activation activity. Functional validation experiments in transgenic plants demonstrated that overexpression of Ar-miR396b inhibited adventitious root growth, whereas overexpression of ArGRF1 increased adventitious root growth. These results help clarify the molecular regulatory mechanisms underlying adventitious root growth in A. rubrum and provide some new insights into the rooting rate in this species.

Temporal and spatial changes in rhizosphere bacterial diversity of mountain Rhododendron mucronulatum.

To better conserve the ecology of the wild Rhododendron mucronulatum range, we studied the rhizosphere microenvironment of R. mucronulatum in Beijing's Yunmeng Mountain National Forest Park. R. mucronulatum rhizosphere soil physicochemical properties and enzyme activities changed significantly with temporal and elevational gradients. The correlations between soil water content (SWC), electrical conductivity (EC), organic matter content (OM), total nitrogen content (TN), catalase activity (CAT), sucrose-converting enzyme activity (INV), and urease activity (URE) were significant and positive in the flowering and deciduous periods. The alpha diversity of the rhizosphere bacterial community was significantly higher in the flowering period than in the deciduous period, and the effect of elevation was insignificant. The diversity of the R. mucronulatum rhizosphere bacterial community changed significantly with the change in the growing period. A network analysis of the correlations revealed stronger linkages between the rhizosphere bacterial communities in the deciduous period than in the flowering period. Rhizomicrobium was the dominant genus in both periods, but its relative abundance decreased in the deciduous period. Changes in the relative abundance of Rhizomicrobium may be the main factor influencing the changes in the R. mucronulatum rhizosphere bacterial community. Moreover, the R. mucronulatum rhizosphere bacterial community and soil characteristics were significantly correlated. Additionally, the influence of soil physicochemical properties on the rhizosphere bacterial community was larger than that of enzyme activity on the bacterial community. We mainly analyzed the change patterns in the rhizosphere soil properties and rhizosphere bacterial diversity of R. mucronulatum during temporal and spatial variation, laying the foundation for further understanding of the ecology of wild R. mucronulatum.

Regulatory Mechanisms of ArAux/IAA13 and ArAux/IAA16 in the Rooting Process of Acer rubrum.

Acer rubrum is difficult to root during cutting propagation. Auxin/indole-acetic acids (Aux/IAA) proteins, which are encoded by the early response genes of auxin, are transcriptional repressors that play important roles in auxin-mediated root growth and development. In this study, ArAux/IAA13 and ArAux/IAA16, which were significantly differentially expressed after 300 mg/L indole butyric acid treatment, were cloned. Heatmap analysis revealed that they might be associated with the process of adventitious root (AR) growth and development mediated by auxin. Subcellular localization analysis showed that they performed their function in the nucleus. Bimolecular fluorescence complementation assays revealed the interactions between them and two auxin response factor (ARF) proteins, ArARF10 and ArARF18, confirming their relevance to AR growth and development. Overexpression of transgenic plants confirmed that the overexpression of ArAux/IAA13 and ArAux/IAA16 inhibited AR development. These results help elucidate the mechanisms of auxin-mediated AR growth and development during the propagation of A. rubrum and provide a molecular basis for the rooting of cuttings.

Key regulatory pathways, microRNAs, and target genes participate in adventitious root formation of Acer rubrum L.

Red maple (Acer rubrum L.) is a type of colorful ornamental tree with great economic value. Because this tree is difficult to root under natural conditions and the seedling survival rate is low, vegetative propagation methods are often used. Because the formation of adventitious roots (ARs) is essential for the asexual propagation of A. rubrum, it is necessary to investigate the molecular regulatory mechanisms of AR formation in A. rubrum. To address this knowledge gap, we sequenced the transcriptome and small RNAs (sRNAs) of the A. rubrum variety 'Autumn Fantasy' using high-throughput sequencing and explored changes in gene and microRNA (miRNA) expression in response to exogenous auxin treatment. We identified 82,468 differentially expressed genes (DEGs) between the treated and untreated ARs, as well as 48 known and 95 novel miRNAs. We also identified 172 target genes of the known miRNAs using degradome sequencing. Two key regulatory pathways (ubiquitin mediated proteolysis and plant hormone signal transduction), Ar-miR160a and the target gene auxin response factor 10 (ArARF10) were selected based on KEGG pathway and cluster analyses. We further investigated the expression patterns and regulatory roles of ArARF10 through subcellular localization, transcriptional activation, plant transformation, qRT-PCR analysis, and GUS staining. Experiments overexpressing ArARF10 and Ar-miR160a, indicated that ArARF10 promoted AR formation, while Ar-miR160a inhibited AR formation. Transcription factors (TFs) and miRNAs related to auxin regulation that promote AR formation in A. rubrum were identified. Differential expression patterns indicated the Ar-miR160a-ArARF10 interaction might play a significant role in the regulation of AR formation in A. rubrum. Our study provided new insights into mechanisms underlying the regulation of AR formation in A. rubrum.

Identification and Analysis of Aux/IAA Family in Acer rubrum.

The phytohormone auxin are important in all aspects of plant growth and development. The Auxin/Indole-3-Acetic Acid (Aux/IAA) gene responds to auxin induction as auxin early response gene family. Despite the physiological importance of the Aux/IAA gene, a systematic analysis of the Aux/IAA gene in Acer rubrum has not been reported. This paper describes the characterization of Acer rubrum Aux/IAA genes at the transcriptomic level and Acer yangbiense Aux/IAA genes at the genomic level, with 17 Acer rubrum AUX/IAA genes (ArAux/IAA) and 23 Acer yangbiense Aux/IAA (AyAux/IAA) genes identified. Phylogenetic analysis shows that AyAux/IAA and ArAux/IAA family genes can be subdivided into 4 groups and show strong evolutionary conservatism. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to test the expression profile of ArAux/IAA genes in different tissues under indole-3-acetic acid (IAA) treatment. Most ArAux/IAA genes are responsive to exogenous auxin and have tissue-specific expression. Overall, these results will provide molecular-level insights into auxin metabolism, transport, and signaling in Acer species.