Auxin and pectin remodeling interplay during rootlet emergence in white lupin

Secondary root emergence is a crucial trait that shapes the plants underground system. Virtually every developmental step of root primordium morphogenesis is controlled by auxin. However, how the hormone controls cell separation in primordium-overlaying tissues through wall loosening is poorly understood. Here, we took advantage of white lupin and its spectacular cluster root development to assess the contribution of auxin to this process. We show that auxin positive role on rootlet emergence is associated with an upregulation of cell wall pectin modifying and degrading genes. Downregulation of a pectinolytic enzyme gene expressed in cells surrounding the primordium resulted in delayed emergence. Pectins were demethylesterified in the emergence zone and auxin treatment further enhanced this effect. Additionally, we report specific rhamnogalacturonan-I modifications during cortical cell separation. In conclusion, we propose a model in which auxin has a dual role during rootlet emergence: Firstly, through active pectin demethylesterification and secondly by regulating the expression of cell wall remodeling enzymes.

A complex regulatory network underlies de novo root regeneration in red maple (Acer rubrum)

Red maple (Acer rubrum L.) is ornamentally and medicinally valuable. However, its wide application is restricted by the difficulty of rooting in cuttings. We analyzed paraffin sections of roots regenerating using RNA-Seq to decipher the mechanisms underlying de novo root regeneration (DNRR) in red maple cuttings. This work contributes to improving the rooting rate and shortening the rooting time. We identified four stages during DNRR: 0 day after induction (DAI), no new cell formation; 30 DAI, root meristem organization; 36 DAI, root primordium formation; and 45 DAI, root elongation growth. We identified 37,959 unigenes by de novo assembly, with 25,477(67.12%) functionally annotated. Furthermore, we identified 1,285 differentially expressed genes (DEGs) between adjacent stages. From GO and KEGG enrichment networks, we found evidence that plant hormones are significant in DNRR of red maple cuttings. Specifically, 149 DEGs functioned in hormone signal transduction pathways, particularly those involving ethylene, auxin, and jasmonic acid (JA). We propose a complex regulatory network model of DNRR in red maple, where wounding induces root regeneration through pathways of JA and auxin signaling. The transcription factors ERF109 and ERF115 integrate JA signal and participate in DNRR directly by regulating SCR activation and indirectly, by promoting auxin biosynthesis.

Transcriptomic profiling and discovery of key genes involved in adventitious root formation from green cuttings of highbush blueberry (Vaccinium corymbosum L.)

Background: Propagation of cuttings is frequently used in various plant species, including blueberry, which shows special root characteristics that may hinder adventitious root (AR) formation. AR formation is influenced by various factors, and auxin is considered to play a central role; however, little is known of the related regulatory mechanisms. In this study, a comparative transcriptome analysis of green cuttings treated with or without indole-butyric acid (IBA) was performed via RNA_seq to identify candidate genes associated with IBA-induced AR formation.Results: Rooting phenotypes, especially the rooting rate, were significantly promoted by exogenous auxin in the IBA application. Blueberry AR formation was an auxin-induced process, during which adventitious root primordium initiation (rpi) began at 14 days after cutting (DAC), root primordium (rp) was developed at 21 DAC, mature AR was observed at 28 DAC and finally outgrowth from the stem occurred at 35 DAC. Higher IAA levels and lower ABA and zeatin contents might facilitate AR formation and development. A time series transcriptome analysis identified 14970 differentially expressed genes (DEGs) during AR formation, of which there were 7467 upregulated and 7503 downregulated genes. Of these, approximately 35 candidate DEGs involved in the auxin-induced pathway and AR formation were further identified, including 10 auxin respective genes (ARFs and SAURs), 13 transcription factors (LOB domain-containing protein (LBDs)), 6 auxin transporters (AUX22, LAX3/5 and PIN-like 6 (PIL6s)) and 6 rooting-associated genes (root meristem growth factor 9 (RGF9), lateral root primordium 1 (LRP1s), and dormancy-associated protein homologue 3 (DRMH3)). All these identified DEGs were highly upregulated in certain stages during AR formation, indicating their potential roles in blueberry AR formation.Conclusions: The transcriptome profiling results indicated candidate genes or major regulatory factors that influence adventitious root formation in blueberry and provided a comprehensive understanding of the rooting mechanism underlying the auxin-induced AR formation from blueberry green cuttings.

Transcriptomic profiling and discovery of key genes involved in adventitious root formation from green cuttings of highbush blueberry (Vaccinium corymbosum L.)

Background: Propagation of cuttings is frequently used in various plant species, including blueberry, which shows special root characteristics that may hinder adventitious root (AR) formation. AR formation is influenced by various factors, and auxin is considered to play a central role; however, little is known of the related regulatory mechanisms. In this study, a comparative transcriptome analysis of green cuttings treated with or without indole-butyric acid (IBA) was performed via RNA_seq to identify candidate genes associated with IBA-induced AR formation. Results: Rooting phenotypes, especially the rooting rate, were significantly promoted by exogenous auxin in the IBA application. Blueberry AR formation was an auxin-induced process, during which adventitious root primordium initiation (rpi) began at 14 days after cutting (DAC), root primordium (rp) was developed at 21 DAC, mature AR was observed at 28 DAC and finally outgrowth from the stem occurred at 35 DAC. Higher IAA levels and lower ABA and zeatin contents might facilitate AR formation and development. A time series transcriptome analysis identified 14970 differentially expressed genes (DEGs) during AR formation, of which there were 7467 upregulated and 7503 downregulated genes. Of these, approximately 35 candidate DEGs involved in the auxin-induced pathway and AR formation were further identified, including 10 auxin respective genes ( ARFs and SAURs ), 13 transcription factors ( LOB domain-containing protein ( LBD s)), 6 auxin transporters ( AUX22 , LAX3/5 and PIN-like 6 ( PIL6s )) and 6 rooting-associated genes ( root meristem growth factor 9 ( RGF9 ), lateral root primordium 1 ( LRP1s ), and dormancy-associated protein homologue 3 ( DRMH3 )). All these identified DEGs were highly upregulated in certain stages during AR formation, indicating their potential roles in blueberry AR formation. Conclusions: The transcriptome profiling results indicated candidate genes or major regulatory factors that influence adventitious root formation in blueberry and provided a comprehensive understanding of the rooting mechanism underlying the auxin-induced AR formation from blueberry green cuttings.

Transcriptomic profiling and discovery of key genes involved in adventitious root formation from green cuttings of highbush blueberry (Vaccinium corymbosum L.)

Background: Propagation of cuttings was mostly used in various plant species including blueberry, the special root characteristics of blueberry usually resulted in a difficulty in adventitious root (AR) formation. The AR formation was influenced by various factors, of which auxin was considered to play a center role, however little is known of the related regulative mechanisms. In this study, a comparative transcriptome analysis using RNA_seq of green cuttings treated with or without IBA was performed to identify candidate genes associated with IBA-induced AR formation. Results: Rooting phenotypes, especially rooting rate, was significantly promoted by exogenous auxin IBA application. Blueberry AR formation was a auxin-induced process, during which the adventitious root primordium initiation (rpi) began to be formed at 14 day after cutting (DAC), developed into root primordium (rp) at 21 DAC, then further developed to mature AR at 28 DAC and finally outgrowth from stem at 35 DAC. Higher IAA level and lower content of ABA and zeatin might facilitate the AR formation and development. A time series transcriptome analysis indentified 14970 differentially expressed genes (DEGs) during AR formation, of which there were 7467 up-regulated and 7503 down-regulated genes, respectively. Of these, about 35 candidate DEGs involved in auxin-induced pathway and AR formation were further identified, including 10 auxin respective genes ARFs and SAURs, 13 transcription factors LOB domain-containing protein (LBDs), 6 auxin transporter AUX22, LAX3/5 and PIN-like 6s (PIL6s) and 6 rooting-associated genes root meristem growth factor 9 (RGF9), lateral root primordium 1 (LRP1s), dormancy-associated protein homolog 3 (DRMH3). All these identified DEGs were highly up-regulated in certain stage during AR formation, indicating their potential roles in blueberry AR formation. Conclusions: The transcriptome profiling indicated candidate genes or major regulative factors that influence adventitious root formation in blueberry, and provided a comprehensive understanding of rooting mechanism of the auxin-induced AR formation from blueberry green cuttings.

Transcriptomic profiling and discovery of key genes involved in adventitious root formation from green cuttings of highbush blueberry (Vaccinium corymbosum L.)

Background Propagation of cuttings was mostly used in various plant species including blueberry, the special root characteristics of blueberry usually resulted in a difficulty in adventitious root (AR) formation. The AR formation was influenced by various factors, of which auxin was considered to play a center role, however little is known of the related regulative mechanisms. In this study, transcriptome analysis using RNA_seq from the stem of green cuttings of southern highbush blueberry 'Biloxi' was performed to discover candidate genes associated with AR formation.Results Rooting phenotypes, especially rooting rate, was significantly promoted by exogenous auxin IBA application. The adventitious root primordium initiation (rpi) began to be formed at 14 day (d) after cutting, developed into root primordium (rp) at 21d, finally the rp further developed to mature AR at 28d. Higher IAA and lower ABA and zeatin might facilitate the AR formation and development. A time series transcriptome analysis indentified 14970 differentially expressed genes (DEGs) during AR formation, of which there were 7467 up-regulated and 7503 down-regulated genes, respectively. Of these, about 35 candidate DEGs involved in auxin-induced pathway and AR formation were further identified, including 10 auxin respective genes ARFs and SAURs , 13 transcription factors LOB domain-containing protein ( LBD s), 6 auxin transporter AUX22 , LAX3/5 and PIN-like 6s ( PIL6s ) and 6 rooting-associated genes root meristem growth factor 9 ( RGF9 ), lateral root primordium 1 ( LRP1s ), dormancy-associated protein homolog 3 ( DRMH3 ). All these identified DEGs were highly up-regulated in certain AR developed stage, indicating their potential roles in blueberry AR formation.Conclusions The transcriptome profiling indicated candidate genes or major regulative factors that influence adventitious root formation in blueberry, and provided a comprehensive understanding of rooting mechanism of the auxin-induced AR formation from blueberry green cuttings.

Unique features of the grapevine VvK5.1 channel support novel functions for outward K+ channels in plants

The unexpected location of VvK5.1 expression detected in the lateral root primordium, berry phloem and pistil provides new insights into the roles that this outward channel type can play in plants.