The Medicago species A2-type cyclin is auxin regulated and involved in meristem formation but dispensable for endoreduplication-associated developmental programs.
Phytohormones as well as temporal and spatial regulation of the cell cycle play a key role in plant development. Here, we investigated the function and regulation of an alfalfa (Medicago sativa) A2-type cyclin in three distinct root developmental programs: in primary and secondary root development, nodule development, and nematode-elicited gall formation. Using transgenic plants carrying the Medsa;cycA2;2 promoter-beta-glucuronidase gene fusion, in combination with other techniques, cycA2;2 expression was localized in meristems and proliferating cells in the lateral root and nodule primordia. Rapid induction of cycA2;2 by Nod factors demonstrated that this gene is implicated in cell cycle activation of differentiated cells developing to nodule primordia. Surprisingly, cycA2;2 was repressed in the endoreduplicating, division-arrested cells both during nodule development and formation of giant cells in nematode-induced galls, indicating that CycA2;2 was dispensable for S-phase in endoreduplication cycles. Overexpression of cycA2;2 in transgenic plants corresponded to wild type protein levels and had no apparent phenotype. In contrast, antisense expression of cycA2;2 halted regeneration of somatic embryos, suggesting a role for CycA2;2 in the formation or activity of apical meristems. Expression of cycA2;2 was up-regulated by auxins, as expected from the presence of auxin response elements in the promoter. Moreover, auxin also affected the spatial expression pattern of this cyclin by shifting the cycA2;2 expression from the phloem to the xylem poles.
Roudier
François
F
Institut des Sciences du Végétale, Centre National de la Recherche Scientiique Unité Propre de Recherche, Gi-sur-Yvette, France.
Fedorova
Elena
E
Lebris
Manuel
M
Lecomte
Phillippe
P
Györgyey
Janos
J
Vaubert
Daniele
D
Horvath
Gabor
G
Abad
Pierre
P
Kondorosi
Adam
A
Kondorosi
Eva
E
D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D019925:Cyclin A / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D007210:Indoleacetic Acids / Q000494:pharmacology*; D029902:Medicago / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D018519:Meristem / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D008938:Mitosis / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D009348:Nematoda / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D010941:Plant Tumors / Q000235:genetics / Q000469:parasitology; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000254:growth & development
D019925:Cyclin A; D007210:Indoleacetic Acids; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D005966:Glucuronidase