主讲人：Ralph S. Quatrano，教授
讲座地点：北大新生物楼101室邓佑才报告厅
讲座日期：2009-03-16
Regulation of polar tip growth and desiccation tolerance in the moss (Physcomitrella patens): the roles of the Arp2/3 & SCAR complexes and ABA & abi3
Ralph S. Quatrano
Department of Biology
Washington University in St. Louis
The components required for protonemal filaments of P. patens to undergo tip growth and division, as well as to perceive and respond to orienting vectors such as light and gravity, are localized in the single apical cell. Actin microfilaments are required for these polar responses. To elucidate the mechanism(s) involved we have taken a candidate gene approach and focused our attention on members of the protein complexes that regulate assembly of the actin network; the Arp2/3 and Wave/SCAR complexes. When either ARPC4 (a member of the ARP2/3 complex) or BRK1 (a member of the Wave/SCAR complex) are deleted by gene targeting, the null mutants (∆arpc4; ∆brk1) are viable and clearly undergo normal morphogenesis into leafy shoots. However, in both cases there is a striking phenotype in filamentous stage, i.e. a drastic reduction of filament elongation. Furthermore, a more severe phenotype is seen in ∆brk1, i.e. smaller and fewer cells with misplaced cross walls compared to the normal protonemal cells or with ∆arpc4. Insertion of YFP-BRK into ∆brk1, and YFP-ARPC4 into ∆arpc4, results in the rescue of mutant phenotypes and the localization of BRK1 and ARPC4 only at the tips of apical cells. Hence, BRK1 and ARPC4 are normally found at the tip of apical cells where their localization appears to be correlated with rapid tip growth of the filaments. Furthermore, we found that in ∆brk1 both ARPC4 and AtRABA4d accumulate in protonemal cells but are not localized to the tip of the apical cell. Our results are consistent with a model that the Arp2/3 and Wave/SCAR complexes function directly or indirectly in the selective accumulation/stabilization of the actin and other proteins required for polar cell growth of filaments at the site of tip elongation, but not for the morphogenesis of the gametophore.
The phytohormone abscisic acid (ABA) and the transcriptional regulator ABI3 play a central role in regulation of seed development and desiccation tolerance during the later stage of embryogenesis. The ABA-response pathway and ABI3 genes are present in P. patens and furthermore, the PpABI3 gene was shown to enhance the expression of ABA-regulated promoters in P. patens only in the presence of ABA. Using both a deletion and overexpression strain of PpABI3, ABA regulated gene expression and ABA inhibition of colony growth were dramatically affected. Based on these results, we suggest that PpABI3 genes are essential for ABA signaling in P. patens similar to its role in seed development. However, expression of PpABI3A driven by the Arabidopsis ABI3 promoter does not restore desiccation tolerance and only partially complements other phenotypes of the Arabidopsis abi3-6 mutant.
REFERENCES
Related Research Articles:
Harries, P., Pan, A., and Quatrano, R. S. (2005). Actin-related protein2/3 complex component ARPC1 is required for proper cell morphogenesis and polarized cell growth in Physcomitrella patens. The Plant Cell 17: 2327-2339.
Lee, K. J. D., Sakata, Y., Mau, S-L., Pettolino, F., Bacic, A., Quatrano, R. S., Knight, C. D., and Knox, J. P. (2005). Arabinogalactan-proteins are required for apical cell extension in the moss Physcomitrella patens. The Plant Cell 17: 3051-3065.
Perroud, P-F., and Quatrano, R. S. (2006). The role of ARPC4 in tip growth and alignment of the polar axis in filaments of Physcomitrella patens. Cell Motility and the Cytoskeleton 63: 162-171.
Marella, H., Sakata, Y., and Quatrano, R. S. (2006). Characterization and functional analysis of ABSCISIC ACID INSENSITIVE3-like genes from Physcomitrella patens. The Plant Journal 46: 1032-1044.
Cuming, A., Cho, S. H., Zhou, Y., Kamisugi, Y., Graham, H., and Quatrano, R. S. (2007). Microarray analysis of transcriptional responses to abscisic acid and osmotic, salt, and drought stress in the moss, Physcomitrella patens. New Phytologist 176: 275-287.
Rensing, S. A., Lang, D., Zimmer, A., Terry, A., Salamov, A., Shapiro, H., Nishiyama, T., Perroud, P-F., et al. (2008). The Physcomitrella genome reveals insights into the conquest of land by plants. Science 319: 64-69. (Corresponding Author – R. Quatrano).
Perroud, P-F. and Quatrano, R.S. (2008). BRICK1 is required for apical cell growth in filaments of the moss Physcomitrella patens but not for gametophore morphology. The Plant Cell 20: 411-422.
Khandelwal, A., Elvitigala, T., Ghosh, B., and Quatrano, R. S. (2008). Arabidopsis transcriptome reveals control circuits regulating redox homeostasis and the role of an AP2 transcription factor. Plant Physiology 148: 2050-2058.
Komatsu, K., Nishikawa,Y., Ohtsuka, T., Taji, T. Quatrano, R.S., Tanaka, S., and Sakata, Y. (2009). Functional analyses of the ABI1-related protein phosphatase type 2C reveal evolutionarily conserved regulation of abscisic acid signaling between Arabidopsis and the moss Physcomitrella patens. Plant Molecular Biology. In Press.
Additional Articles and Reviews:
Cove, D. J., Bezanilla, M., Harries, P., and Quatrano, R. S. (2006). Mosses as model systems for the study of metabolism and development. Annual Review of Plant Biology 57: 497-520.
Quatrano, R. S., McDaniel, S. F., Khandelwal, A., Perroud, P-F., and Cove, D. J. (2007). Physcomitrella patens: mosses enter the genomic age. Current Opinion in Plant Biology 10: 182-189.
Cho, S. H., von Schwartzenberg, K., and Quatrano, R. S. (2009). The role of abscisic acid in stress tolerance. IN: The Moss Physcomitrella. (Eds: C. D. Knight, D. J. Cove and P.-F. Perroud). Chapter 11, pp. 282-293. Wiley Blackwell (Oxford).
Rock, C.D., Sakata, Y., and Quatrano, R. S. (2009).The Role of Abscisic Acid. IN:Abiotic Stress Adaptation in Plants: Physiological, Molecular and Genomic Foundation. In Press. (Eds: A. Pareek, S.K. Sopory, H.J. Bohnert and Govindjee). Springer, Dordrecht.
Charron, A., and Quatrano, R. S. (2009). Between a rock and a dry place: the water-stressed moss. Molecular Plant. In Press.
