Molecular Cloning and Sequence Analysis of Expansins-a Highly Conserved, Multigene Family of Proteins that Mediate Cell Wall Extension in Plants

Expansins are unusual proteins discovered by virtue of their ability to mediate cell wall extension in plants. We identified cDNA clones for two cucumber expansins on the basis of peptide sequences of proteins purified from cucumber hypocotyls. The expansin cDNAs encode related proteins with signal...

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Published in:	Proceedings of the National Academy of Sciences - PNAS 1995-09, Vol.92 (20), p.9245-9249
Main Authors:	Shcherban, Tatyana Y., Shi, Jun, Durachko, Daniel M., Guiltinan, Mark J., McQueen-Mason, Simon J., Shieh, Mark, Cosgrove, Daniel J.
Format:	Article
Language:	eng
Subjects:	Allergens Amino Acid Sequence Amino acids Arabidopsis Base Sequence Biology Blotting, Western Cell Wall - metabolism Cell walls Cloning, Molecular Complementary DNA Conserved Sequence Cucumbers Cucumis sativus Cucumis sativus - genetics Cucumis sativus - metabolism Deoxyribonucleic acid DNA DNA Primers DNA, Complementary Flowers & plants Genes, Plant Hypocotyls Molecular Sequence Data Multigene Family Oryza sativa Phylogeny Plant Proteins - biosynthesis Plant Proteins - genetics Plant Proteins - isolation & purification Plants Plants - classification Plants - genetics Pollen Polymerase Chain Reaction Protein Biosynthesis Proteins Rice Sequence Homology, Amino Acid Space life sciences
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Summary:	Expansins are unusual proteins discovered by virtue of their ability to mediate cell wall extension in plants. We identified cDNA clones for two cucumber expansins on the basis of peptide sequences of proteins purified from cucumber hypocotyls. The expansin cDNAs encode related proteins with signal peptides predicted to direct protein secretion to the cell wall. Northern blot analysis showed moderate transcript abundance in the growing region of the hypocotyl and no detectable transcripts in the nongrowing region. Rice and Arabidopsis expansin cDNAs were identified from collections of anonymous cDNAs (expressed sequence tags). Sequence comparisons indicate at least four distinct expansin cDNAs in rice and at least six in Arabidopsis. Expansins are highly conserved in size and sequence (60-87% amino acid sequence identity and 75-95% similarity between any pairwise comparison), and phylogenetic trees indicate that this multigene family formed before the evolutionary divergence of monocotyledons and dicotyledons. Sequence and motif analyses show no similarities to known functional domains that might account for expansin action on wall extension. A series of highly conserved tryptophans may function in expansin binding to cellulose or other glycans. The high conservation of this multigene family indicates that the mechanism by which expansins promote wall extension tolerates little variation in protein structure.
ISSN:	0027-8424 1091-6490