This Article Full Text (PDF) PPT slides of all figures All Versions of this Article: 21/4/1027    most recent tpc.109.210410v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Cell Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Mach, J. Search for Related Content PubMed PubMed Citation Articles by Mach, J. Agricola Articles by Mach, J.

IN BRIEF

Rice Axillary Meristem Formation Requires Directional Movement of LAX PANICLE1 Protein

Science Editor

jmach{at}aspb.org

The architecture of grasses is dictated by the development of axillary meristems (AMs), which specify the formation of tillers during vegetative growth and the formation of branches and spikelets (short floret-bearing branches) in the inflorescence during reproductive growth. AM initiation and branch development are regulated by developmental, environmental, and hormonal inputs (reviewed in Barazesh and McSteen, 2008). Understanding the regulation of AM formation is essential to improving grain crops, as tillering and inflorescence structure directly affect grain yield.

Genetic factors affect both initiation and outgrowth of the AM, and several mutants are known that specifically perturb AM formation without affecting other meristems. Oikawa and Kyozuka (pages 1095–1108) examine gene function in AM formation in one such mutant in rice, lax panicle1 (lax1). LAX1 encodes a bHLH transcription factor, and lax1 mutant plants have severely reduced branching, both in vegetative and reproductive growth. The authors characterize AM formation using an extensive series of markers; for example, they use OSH1 (Oryza sativa Homebox1) gene expression as a marker of meristematic activity and find that determination as meristematic tissue occurs slightly after the AM appears distinct from the shoot apical meristem (SAM). Examination of these markers in the lax1-2 null mutant showed that these plants can initiate AM formation, but LAX1 function is required to maintain and continue AM growth. The authors also examined the interaction of LAX1 with MONOCULM1 (MOC1), another gene required for branching. Double lax1 moc1 mutants showed an additive phenotype with even more severely reduced branching than the single mutants, indicating that multiple pathways control branching in rice vegetative and reproductive growth.

Intriguingly, LAX1 mRNA is not expressed in the developing AM, but is confined to the junction between the AM and the SAM (see figure , left). However, LAX1 protein acts in the AM, and GFP:LAX1 fusion proteins can be seen in the developing AM (figure, right), indicating that the protein moves into the AM. Moreover, the protein moves only toward the AM; movement toward the SAM is not seen. LAX1 protein movement into the AM is required for its full function: LAX1 fused to a single copy of GFP moves into the AM and can complement the lax1 phenotype, but LAX1 fused to three copies of GFP remains in the boundary region and provides only limited complementation of the lax1 branching defects. Limitation of LAX1 by size indicates that this protein passes through the plasmodesmata under the size exclusion limit; similar cell-to-cell movement has been seen for GFP and the transcription factor LEAFY (reviewed in Gallagher and Benfey, 2005). However, the authors also show that LAX1 protein localizes to the nucleus, where it would not be able to diffuse freely, indicating that other factors may affect its movement. Thus, this important regulator of AM maintenance is localized both by cell type–specific gene expression and protein movement; examination of the mechanisms for LAX1 movement will prove an interesting subject for future research.

View larger version (53K): [in this window] [in a new window] [as a PowerPoint slide]   LAX1 in developing axillary meristems. Left: LAX1 mRNA detected by in situ hybridization. Right: LAX1 protein detected as a GFP fusion (green), with FM4-64–stained plasma membrane (blue). Compare the mRNA and protein localizations at a key developmental stage (black arrowhead at left and white arrowhead at right). Bars = 50 µm.

www.plantcell.org/cgi/doi/10.1105/tpc.109.210410

REFERENCES

Barazesh, S., and McSteen, P. (2008). Hormonal control of grass inflorescence development. Trends Plant Sci. 13: 656–662.[CrossRef][Web of Science][Medline]

Gallagher, K.L., and Benfey, P.N. (2005). Not just another hole in the wall: Understanding intercellular protein trafficking. Genes Dev. 19: 189–195.[Abstract/Free Full Text]

Oikawa, T., and Kyozuka, J. (2009). Two-step regulation of LAX PANICLE1 protein accumulation in axillary meristem formation in rice. Plant Cell 21: 1095–1108.[Abstract/Free Full Text]

Related articles in Plant Cell:

Two-Step Regulation of LAX PANICLE1 Protein Accumulation in Axillary Meristem Formation in Rice

Tetsuo Oikawa and Junko Kyozuka
Plant Cell 2009 21: 1095-1108. [Abstract] [Full Text]  

This Article Full Text (PDF) PPT slides of all figures All Versions of this Article: 21/4/1027    most recent tpc.109.210410v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Cell Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Mach, J. Search for Related Content PubMed PubMed Citation Articles by Mach, J. Agricola Articles by Mach, J.