First published online March 1, 2007
Development 134, 601e (2007)
© The Company of Biologists Limited
Phyllotactic patterning: microRNAs made redundant?
Plant microRNAs regulate gene expression in a sequence-specific manner by
binding to target mRNAs, leading to their degradation. Unlike animal
microRNAs, plant microRNAs have a high degree of complementarity to their
targets, and the scarcity of microRNA loss-of-function phenotypes in plants
implies that redundancy exists between microRNA family members. Now, two
papers provide new insights into this redundancy and into microRNA-regulated
shoot development in Arabidopsis. Elliot Meyerowitz and colleagues
show how the activity of redundant miR164 family members is crucial
for the spatial positioning of flowers on the Arabidopsis stem, and
for the number and size of floral organs (see
p. 1051). And Patrick
Laufs and co-workers on p.
1045 report how the continued expression of CUP-SHAPED
COTYLEDON2 (CUC2), a miR164 target, regulates correct
flower positioning. In their study, Meyerowitz and colleagues report that the
elimination of all three, but not of individual, miR164 family
members severely disrupts flower and shoot development in
Arabidopsis. In the absence of the three miR164 microRNAs,
the expression domains of their transcription factor-encoding targets,
CUC1 and CUC2, become enlarged in the inflorescence
meristems of mutant plants. This result, together with other findings reported
here, indicate that the miR164 microRNAs not only act to reduce
target transcript levels but can also spatially limit target mRNA accumulation
- functions, the authors propose, that hint at their possible involvement in
developmental robustness. The study also reveals that the miR164
family members are not fully redundant but show some functional
diversification, raising questions as to whether microRNA gene families evolve
in the same way as protein-coding gene families do through gene or genome
duplication. Laufs and co-workers' complementary study shows that the
miR164-regulated expression of CUC2 is crucial for organ
patterning in the stem rather than in the apical meristem. They report that
the pattern of flower primordia is irregular in the fully grown stems of
plants that express a miR164-resistant version of CUC2.
These plants effectively overexpress CUC2, indicating that the timing
and level of CUC2 expression is crucial for patterning. Together,
these results indicate that patterning is not completely determined in the
apical meristem and that redundancy between microRNAs provides the platform
for this unexpected level of complexity.
Related articles in Development:
- Plants expressing a miR164-resistant CUC2 gene reveal the importance of post-meristematic maintenance of phyllotaxy in Arabidopsis
- Alexis Peaucelle, Halima Morin, Jan Traas, and Patrick Laufs
Development 2007 134: 1045-1050.
[Abstract]
[Full Text]
- Redundancy and specialization among plant microRNAs: role of the MIR164 family in developmental robustness
- Patrick Sieber, Frank Wellmer, Jacqueline Gheyselinck, José Luis Riechmann, and Elliot M. Meyerowitz
Development 2007 134: 1051-1060.
[Abstract]
[Full Text]
