Localized upregulation of a new expansin gene predicts the site of leaf formation in the tomato meristem.
Expansins are extracellular proteins that increase plant cell wall extensibility in vitro and are thought to be involved in cell expansion. We showed in a previous study that administration of an exogenous expansin protein can trigger the initiation of leaflike structures on the shoot apical meristem of tomato. Here, we studied the expression patterns of two tomato expansin genes, LeExp2 and LeExp18. LeExp2 is preferentially expressed in expanding tissues, whereas LeExp18 is expressed preferentially in tissues with meristematic activity. In situ hybridization experiments showed that LeExp18 expression is elevated in a group of cells, called I1, which is the site of incipient leaf primordium initiation. Thus, LeExp18 expression is a molecular marker for leaf initiation, predicting the site of primordium formation at a time before histological changes can be detected. We propose a model for the regulation of phyllotaxis that postulates a crucial role for expansin in leaf primordium initiation.
Institute of Plant Physiology, University of Berne, Altenbergrain 21, CH-3013 Berne, Switzerland.
D
D
Reinhardt
F
F
Wittwer
T
T
Mandel
C
C
Kuhlemeier
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D017403:In Situ Hybridization; D018551:Solanum lycopersicum / Q000235:genetics* / Q000254:growth & development*; D018519:Meristem / Q000254:growth & development; D008954:Models, Biological; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D015854:Up-Regulation
D017931:DNA Primers; D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; C095825:expansin protein, plant