Abstract
Small peptides of the Arabidopsis GLV/RGF/CLEL family are involved in different developmental programmes, including meristem maintenance and gravitropic responses. In addition, our previous report suggested that they also participate in the formation of lateral roots. Specifically, GLV6 is transcribed during the first stages of primordium development and GLV6 overexpression results in a strong reduction of emerged lateral roots. To investigate the cause of this phenotype we analysed primordium development in gain-of-function (gof) mutants and found that GLV6 induces supernumerary pericycle divisions, hindering the formation of a dome-shaped primordium, a prerequisite for successful emergence. The GLV6 phenotype could be reproduced by ectopic expression of the gene only in xylem-pole pericycle cells. Furthermore, GLV6 seems to function at the very beginning of lateral root initiation because GLV6 excess—either gene overexpression or peptide treatment—disrupts the first asymmetric cell divisions required for proper primordium formation. Our results suggest that GLV6 acts during lateral root initiation controlling the patterning of the first pericycle divisions.
Highlights
Unlike animals, plant organs are initiated in the meristems during post-embryonic development
We showed in a recent report that the overexpression of several GLV genes results in a strong decrease in emerged lateral root (ELR) density as observed independently by another research group for GLV1/CLEL6 and GLV10/CLEL8 (Meng et al, 2012)
Based on the characterization of promoter-reporter lines, we have previously shown that GLV6 is transcribed in the root apical meristem (RAM) and is the first GLV transcript detected during primordium formation (Fernandez et al, 2013a)
Summary
Plant organs are initiated in the meristems during post-embryonic development. Meristematic cells proliferate in an undifferentiated state and produce differentiating cell lineages that eventually give rise to new lateral organs. This process is highly regulated and relies on a complex network of genetic and hormonal cues. Specific pericycle cells at the xylem pole retain the capacity to resume meristematic activity after leaving the root apical. As the main root keeps growing, some xylem pole pericycle (XPP) cells undergo a sequence of events resulting in the formation of a novel lateral root primordium (LRP), followed by the emergence of the lateral root (LR) out of the main root tissues
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