COP1 mediates the coordination of root and shoot growth by light through modulation of PIN1 and PIN2-dependent auxin transport in Arabidopsis

by Sassi, M, Lu, Y, Zhang, YH, Wang, J, Dhonukshe, P, Blilou, I Dai, MQ, Li, J, Gong, XM, Jaillais, Y, Yu, XH, Traas, J, Ruberti, I, Wang, HY, Scheres, B, Vernoux, T and Xu, Jian

Development 139, 3402-3412 (2012)

Although the roots of most plant species are not directly exposed to light, root growth is controlled by light and integrated with the growth of above-ground organs. We uncover a novel long-distance mechanism by which light signals through the master photomorphogenesis repressor COP1 to coordinate root and shoot development in Arabidopsis. We show that, in the shoot, COP1 regulates shoot-to-root transport of auxin by controlling transcription of the auxin efflux carrier gene PIN-FORMED1 (PIN1). Whereas in the root apical meristem COP1 regulates auxin transport and cell proliferation by modulating the intracellular distribution of PIN1 and PIN2 in the root, thereby ensuring rapid and precise tuning of root growth to the light environment.

Together, our results identify auxin as a long-distance signal in light-regulated plant development and show how spatially separated control mechanisms can converge on a single signalling system to coordinate development at the whole plant level.

Read online: Pubmed.

Learn more about Jian Xu’s research.

A col10a1: nlGFP transgenic line displays putative osteoblast precursors at the medaka notochordal sheath prior to mineralization

by Joerg Renn, Anita Büttner, Thuy Thanh To, Sherlynn Jin Hui Chan and Christoph Winkler

Dev Biol 2013 Sep 1;381(1):134-43

In teleosts, such as medaka, ossification of the vertebral column starts with the mineralization of the notochordal sheath in a segmental pattern. This establishes the chordal centrum, which serves as the basis for further ossifications by sclerotome derived osteoblasts generating the vertebral body.

So far, it is unclear which cells produce the notochordal sheath and how a segmental pattern of mineralization is established in teleosts. Here, we use a transgenic medaka line that expresses nlGFP under the control of the col10a1 promoter for in vivo analysis of vertebral body formation. We show that col10a1:nlGFP expression recapitulates endogenous col10a1 expression.

In the axial skeleton, col10a1:nlGFP cells appear prior to the mineralization of the notochordal sheath in a segmental pattern. These cells remain on the outer surface of the chordal centra during mineralization as well as subsequent perichordal ossification of the vertebral bodies. Using twist1a1:dsRed and osx:mCherry transgenic lines we show that a subset of col10a1:nlGFP cells is derived from sclerotomal precursors and differentiates into future osteoblasts.

For the first time, this shows a segmental occurrence of putative osteoblast precursors in the vertebral centra prior to ossification of the notochordal sheath. This opens the possibility that sclerotome derived cells in teleosts are implicated in the establishment of the mineralized vertebral column in a similar manner as previously described for tetrapods.

Read online: Pubmed.

Learn more about Christoph Winkler’s research.

Chromatin in a marine picoeukaryote is a disordered assemblage of nucleosomes

by Lu Gan,  Mark S Ladinsky, and Grant J Jensen

Chromosoma 2013 Jul 3

Chromatin organization is central to many conserved biological processes, but it is generally unknown how the underlying nucleosomes are arranged in situ. Here, we have used electron cryotomography to study chromatin in the picoplankton Ostreococcus tauri, the smallest known free-living eukaryote.

By visualizing the nucleosome densities directly, we find that O. tauri chromosomes do not arrange into discrete, compact bodies or any other higher level of order. In contrast to the textbook 30-nm-fiber model, O. tauri chromatin resembles a disordered assemblage of nucleosomes akin to the polymer-melt model. This disorganized nucleosome arrangement has important implications for potentially conserved functions in tiny eukaryotes such as the clustering of non-homologous chromosomes at the kinetochore during mitosis and the independent regulation of closely positioned adjacent genes.

Read online: Springer.

Learn more about Lu Gan’s research.