Auxin and cytokinin control formation of the quiescent centre in the adventitious root apex of Arabidopsis.
OBJECTIVE
Adventitious roots (ARs) are part of the root system in numerous plants, and are required for successful micropropagation. In the Arabidopsis thaliana primary root (PR) and lateral roots (LRs), the quiescent centre (QC) in the stem cell niche of the meristem controls apical growth with the involvement of auxin and cytokinin. In arabidopsis, ARs emerge in planta from the hypocotyl pericycle, and from different tissues in in vitro cultured explants, e.g. from the stem endodermis in thin cell layer (TCL) explants. The aim of this study was to investigate the establishment and maintenance of the QC in arabidopsis ARs, in planta and in TCL explants, because information about this process is still lacking, and it has potential use for biotechnological applications.


METHODS
Expression of PR/LR QC markers and auxin influx (LAX3)/efflux (PIN1) genes was investigated in the presence/absence of exogenous auxin and cytokinin. Auxin was monitored by the DR5::GUS system and cytokinin by immunolocalization. The expression of the auxin-biosynthetic YUCCA6 gene was also investigated by in situ hybridization in planta and in AR-forming TCLs from the indole acetic acid (IAA)-overproducing superroot2-1 mutant and its wild type.


RESULTS
The accumulation of auxin and the expression of the QC marker WOX5 characterized the early derivatives of the AR founder cells, in planta and in in vitro cultured TCLs. By determination of PIN1 auxin efflux carrier and LAX3 auxin influx carrier activities, an auxin maximum was determined to occur at the AR tip, to which WOX5 expression was restricted, establishing the positioning of the QC. Cytokinin caused a restriction of LAX3 and PIN1 expression domains, and concomitantly the auxin biosynthesis YUCCA6 gene was expressed in the apex.


CONCLUSIONS
In ARs formed in planta and TCLs, the QC is established in a similar way, and auxin transport and biosynthesis are involved through cytokinin tuning.
Department of Environmental Biology, Sapienza University of Rome, Italy.
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Della Rovere
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Fattorini
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D'Angeli
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Veloccia
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Falasca
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Altamura
D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D015415:Biomarkers / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D005966:Glucuronidase / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development; D007210:Indoleacetic Acids / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D007541:Isopentenyladenosine / Q000031:analogs & derivatives / Q000378:metabolism; D007701:Kinetin / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D018517:Plant Roots / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development; D015026:Zeatin / Q000494:pharmacology
D029681:Arabidopsis Proteins; D015415:Biomarkers; D003583:Cytokinins; D018398:Homeodomain Proteins; D007210:Indoleacetic Acids; D007211:Indoles; C531125:LAX3 protein, Arabidopsis; D026901:Membrane Transport Proteins; C116363:PIN1 protein, Arabidopsis; C116421:WUSCHEL protein, Arabidopsis; C014612:indolebutyric acid; D007541:Isopentenyladenosine; D015026:Zeatin; C009699:zeatin riboside; D006899:Mixed Function Oxygenases; C562183:YUCCA6 protein, Arabidopsis; D005966:Glucuronidase; D007701:Kinetin
Adventitious root apex; Arabidopsis thaliana; WOX5; auxin biosynthesis; auxin transport; cytokinin localization; quiescent centre; root meristemoids; stem endodermis; thin cell layers