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First published online January 30, 2009; 10.1105/tpc.108.210113

The Plant Cell 21:16

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IN BRIEF

Breaking Up Is Hard to Do: Cell Separation Events Involve Multiple Polygalacturonases and Multiple Hormones

Nancy R. Hofmann

Science Editor

nhofmann{at}aspb.org

Cell separation events, including abscission (the shedding of an organ) and dehiscence (the release of an organ's contents), take place throughout plant development (reviewed in Lewis et al., 2006Go). Both abscission and dehiscence involve breakdown of the cell wall material between adjacent cells, and it is likely that polygalacturonases (PGs) are involved. A study by Ogawa et al. (pages 216–233) now provides compelling evidence that this is so and that the regulation of cell separation events involves combinations of at least three related PGs and three hormones. The authors cloned a putative PG from Arabidopsis thaliana that, when overexpressed, causes flowers that do not open, atypical petals, and anthers that fail to dehisce normally. Plants lacking this protein had fused pollen (see figure ), and the authors determined that this PG is QUARTET2 (QRT2), which had not been cloned before but was named for the pollen defect of the qrt2 mutant, in which microspores remain in tetrads (Preuss et al., 1994Go). Ogawa et al. found that QRT2 and the closely related proteins ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE1 (ADPG1) and ADPG2 all have in vitro or in planta PG activity and thus are functional PGs.


Figure 1
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  		Cell separation defects in PG mutants. Unlike those from the wild type, siliques from plants lacking ADPG1 fail to dehisce normally (A). The adpg1 adpg2 qrt2 triple mutant exhibits delayed anther dehiscence (B) and the fused pollen tetrads (C) that are characteristic of qrt2 single mutants. (Adapted from Figure 2 of Ogawa et al. [2009]Go.)

 
When Ogawa et al. examined plants lacking QRT2, ADPG1, and/or ADPG2 for defects in cell separation events, they put together an interesting combinatorial picture. All three proteins are involved, and partially redundant, in anther dehiscence (see figure), while ADPG1 and ADPG2 are partially redundant in pod shatter (silique dehiscence), and ADPG2 and QRT2 are partially redundant in floral organ abscission. The expression patterns of the genes lend support to these conclusions. To see whether expression patterns alone can provide specificity for PGs, the authors tested the abilities of various constructs to complement the adpg1 adpg2 qrt2 triple mutant pod shatter phenotype. While ADPG1 driven by its own promoter restored pod shatter to the wild type, QRT2 driven by the same promoter only partially complemented the mutant, and another, less closely related, PG did not complement it at all. Therefore, in addition to different expression patterns, individual PGs appear to show substrate specificity.

Ogawa et al. went on to provide evidence that ethylene, jasmonic acid, and abscisic acid are all needed to promote normal QRT2 expression and floral organ abscission. The data in this study point to a complex, but unified, view of cell separation events, in which PG involvement is shared, but specific PGs take part in different abscission/dehiscence events and individual events can involve several PGs and multiple hormone signals.

Footnotes

www.plantcell.org/cgi/doi/10.1105/tpc.108.210113

REFERENCES

Lewis, M.W., Leslie, M.E., and Liljegren, S.J. (2006). Plant separation: 50 ways to leave your mother. Curr. Opin. Plant Biol. 9: 59–65.[CrossRef][Web of Science][Medline]

Ogawa, M., Kay, P., Wilson, S., and Swain, S.M. (2009). ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE1 (ADPG1), ADPG2, and QUARTET2 are polygalacturonases required for cell separation during reproductive development in Arabidopsis. Plant Cell 21: 216–233.

Preuss, D., Rhee, S.Y., and Davis, R.W. (1994). Tetrad analysis possible in Arabidopsis with mutation of the QUARTET (QRT) genes. Science 264: 1458–1460.[Abstract/Free Full Text]


Related articles in Plant Cell:

ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE1 (ADPG1), ADPG2, and QUARTET2 Are Polygalacturonases Required for Cell Separation during Reproductive Development in Arabidopsis
Mikihiro Ogawa, Pippa Kay, Sarah Wilson, and Stephen M. Swain
Plant Cell 2009 21: 216-233. [Abstract] [Full Text]  




This Article
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tpc.108.210113v1
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