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Background: The DELLA proteins, a class of GA signaling repressors, belong to the GRAS family of plant-specific nuclear proteins. Members of DELLA gene family encode transcriptional regulators with diverse functions in plant development and abiotic stress responses. To date, DELLAs have been identified in various plant species, such as Arabidopsis thaliana, Malus domestica, Populus trichocarpa, and other land plants. Most information of DELLA family genes was obtained from A. thaliana, whereas little is known about the DELLA gene family in blueberry., Results: In this study, we identified three DELLA genes in blueberry (Vaccinium darrowii, VdDELLA) and provided a complete overview of VdDELLA gene family, describing chromosome localization, protein properties, conserved domain, motif organization, and phylogenetic analysis. Three VdDELLA members, containing two highly conserved DELLA domain and GRAS domain, were distributed across three chromosomes. Additionally, cis-acting elements analysis indicated that VdDELLA genes might play a critical role in blueberry developmental processes, hormone, and stress responses. Expression analysis using quantitative real-time PCR (qRT-PCR) revealed that all of three VdDELLA genes were differentially expressed across various tissues. VdDELLA2 was the most highly expressed VdDELLA in all denoted tissues, with a highest expression in mature fruits. In addition, all of the three VdDELLA genes actively responded to diverse abiotic stresses. Based on qRT-PCR analysis, VdDELLA2 might act as a key regulator in V. darrowii in response to salt stress, whereas VdDELLA1 and VdDELLA2 might play an essential role in cold stress response. Under drought stress, all of three VdDELLA genes were involved in mediating drought response. Furthermore, their transiently co-localization with nuclear markers in A. thaliana protoplasts demonstrated their transcriptional regulator roles., Conclusions: In this study, three VdDELLA genes were identified in V. darrowii genome. Three VdDELLA genes were closely related to the C. moschata DELLA genes, S. lycopersicum DELLA genes, and M. domestica DELLA genes, respectively, indicating their similar biological functions. Expression analysis indicated that VdDELLA genes were highly efficient in blueberry fruit development. Expression patterns under different stress conditions revealed the differentially expressed VdDELLA genes responding to salt, drought, and cold stress. Overall, these results enrich our understanding of evolutionary relationship and potential functions of VdDELLA genes, which provide valuable information for further studies on genetic improvement of the plant yield and plant resistance., (© 2024. The Author(s).)

Growth-regulating factors (GRFs) are important regulators of plant development and growth, but their possible roles in xylem development in woody plants remain unclear. Here, we report that Populus alba × Papulus glandulosa PagGRF12a negatively regulates xylem development in poplar. PagGRF12a is expressed in vascular tissues. Compared to non-transgenic control plants, transgenic poplar plants overexpressing PagGRF12a exhibited reduced xylem width and plants with repressed expression of PagGRF12a exhibited increased xylem width. Xylem NAC domain 1 (XND1) encodes a NAC domain transcription factor that regulates xylem development and transcriptional analyses revealed that PagXND1a is highly upregulated in PagGRF12a-overexpressing plants and downregulated in PagGRF12a-suppressed plants, indicating that PagGRF12a may regulate xylem development through PagXND1a. Transient transcriptional assays and chromatin immunoprecipitation-polymerase chain reaction assays confirmed that PagGRF12a directly upregulates PagXND1a. In addition, PagGRF12a interacts with the GRF-Interacting Factor (GIF) PagGIF1b, and this interaction enhances the effects of PagGRF12a on PagXND1a. Our results indicate that PagGRF12a inhibits xylem development by upregulating the expression of PagXND1a., (© 2021 Institute of Botany, Chinese Academy of Sciences.)

Wood formation is the terminal differentiation of xylem mother cells derived from cambial initials, and negative regulators play important roles in xylem differentiation. The molecular mechanism of the negative regulator of xylem differentiation PagKNAT2/6b was investigated. PagKNAT2/6b is an ortholog of Arabidopsis KNAT2 and KNAT6 that is highly expressed in phloem and xylem. Compared to nontransgenic control plants, transgenic poplar plants overexpressing PagKNAT2/6b present with altered vascular patterns, characterized by decreased secondary xylem with thin cell walls containing less cellulose, xylose and lignin. RNA sequencing analyses revealed that differentially expressed genes are enriched in xylem differentiation and secondary wall synthesis functions. Expression of NAM/ATAF/CUC (NAC) domain genes including PagSND1-A1, PagSND1-A2, PagSND1-B2 and PagVND6-C1 is downregulated by PagKNAT2/6b, while PagXND1a is directly upregulated. Accordingly, the dominant repression form of PagKNAT2/6b leads to increased xylem width per stem diameter through downregulation of PagXND1a. PagKNAT2/6b can inhibit cell differentiation and secondary wall deposition during wood formation in poplar by modulating the expression of NAC domain transcription factors. Direct activation of PagXND1a by PagKNAT2/6b is a key node in the negative regulatory network of xylem differentiation by KNOXs., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

Growth-regulating factors (GRFs) are involved in various developmental events, particularly leaf development. However, the functions of GRFs in woody plants remain elusive. In this study, functional characterization of GRF15 in Populus was performed. Most GRFs are preferentially expressed in young leaves. As GRF15 was expressed at the highest level and with highest ratio in Populus species with large leaves, this gene was investigated through transgenic analyses. Promotor-β-glucuronidase analysis revealed expression of GRF15 at the leaf expansion zone. Additionally, GRF15 was found to be localized in the nucleus and regulated by miR396. Leaf size and palisade cell size were significantly increased and decreased in GRF15-overexpressing and dominant repression lines, respectively. Consistently, expression of EXPA11a, a homolog of cell-expansion marker EXPA11 in Arabidopsis, was strongly upregulated and downregulated in the GRF15-overexpressing and dominant repression lines, respectively, which was further manifested by activation of EXPA11a by GRF15 in transactivation assays. Therefore, GRF15 is required for leaf size control and primarily modulates cell expansion during leaf development in Populus., (© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Adventitious roots occur naturally in many species and can also be induced from explants of some tree species including Populus, providing an important means of clonal propagation. Auxin has been identified as playing a crucial role in adventitious root formation, but the associated molecular regulatory mechanisms need to be elucidated. In this study, we examined the role of PagFBL1, the hybrid poplar (Populus alba × P. glandulosa clone 84K) homolog of Arabidopsis auxin receptor TIR1, in adventitious root formation in poplar. Similar to the distribution pattern of auxin during initiation of adventitious roots, PagFBL1 expression was concentrated in the cambium and secondary phloem in stems during adventitious root induction and initiation phases, but decreased in emerging adventitious root primordia. Overexpressing PagFBL1 stimulated adventitious root formation and increased root biomass, while knock-down of PagFBL1 transcript levels delayed adventitious root formation and decreased root biomass. Transcriptome analyses of PagFBL1 overexpressing lines indicated that an extensive remodelling of gene expression was stimulated by auxin signalling pathway during early adventitious root formation. In addition, PagIAA28 was identified as downstream targets of PagFBL1. We propose that the PagFBL1-PagIAA28 module promotes adventitious rooting and could be targeted to improve Populus propagation by cuttings., (© 2018 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)