The miR156 juvenility factor and PLETHORA 2 form a regulatory network and influence timing of meristem growth and lateral root emergence.

Plants develop throughout their lives: seeds become seedlings that mature and form fruits and seeds. Although the underlying mechanisms that drive these developmental phase transitions have been well elucidated for shoots, the extent to which they affect the root is less clear. However, root anatomy does change as some plants mature; meristems enlarge and radial thickening occurs. Here, in Arabidopsis thaliana, we show that overexpressing miR156A, a gene that promotes the juvenile phase, increased the density of the root system, even in grafted plants in which only the rootstock had the overexpression genotype. In the root, overexpression of miR156A resulted in lower levels of PLETHORA 2, a protein that affects formation of the meristem and elongation zone. Crossing in an extra copy of PLETHORA 2 partially rescued the effects of miR156A overexpression on traits affecting root architecture, including meristem length and the rate of lateral root emergence. Consistent with this, PLETHORA 2 also inhibited the root-tip expression of another miR156 gene, miR156C. We conclude that the system driving phase change in the shoot affects developmental progression in the root, and that PLETHORA 2 participates in this network.

Botany: a record-breaking pollen catapult.

The release of stored elastic energy often drives rapid movements in animal systems, and plant components employing this mechanism should be able to move with similar speed. Here we describe how the flower stamens of the bunchberry dogwood (Cornus canadensis) rely on this principle to catapult pollen into the air as the flower opens explosively. Our high-speed video observations show that the flower opens in less than 0.5 ms--to our knowledge, the fastest movement so far recorded in a plant.

FQR1, a novel primary auxin-response gene, encodes a flavin mononucleotide-binding quinone reductase.

FQR1 is a novel primary auxin-response gene that codes for a flavin mononucleotide-binding flavodoxin-like quinone reductase. Accumulation of FQR1 mRNA begins within 10 min of indole-3-acetic acid application and reaches a maximum of approximately 10-fold induction 30 min after treatment. This increase in FQR1 mRNA abundance is not diminished by the protein synthesis inhibitor cycloheximide, demonstrating that FQR1 is a primary auxin-response gene. Sequence analysis reveals that FQR1 belongs to a family of flavin mononucleotide-binding quinone reductases. Partially purified His-tagged FQR1 isolated from Escherichia coli catalyzes the transfer of electrons from NADH and NADPH to several substrates and exhibits in vitro quinone reductase activity. Overexpression of FQR1 in plants leads to increased levels of FQR1 protein and quinone reductase activity, indicating that FQR1 functions as a quinone reductase in vivo. In mammalian systems, glutathione S-transferases and quinone reductases are classified as phase II detoxification enzymes. We hypothesize that the auxin-inducible glutathione S-transferases and quinone reductases found in plants also act as detoxification enzymes, possibly to protect against auxin-induced oxidative stress.