Molecular bases for phyllomorph development in a one-leaf plant,Monophyllaea glabra.
OBJECTIVE
The aboveground part of one-leaf plants (Gesneriaceae) consists of a unique shoot-like unit called a phyllomorph, which is composed of a growing lamina and one petiolode (a stem- and petiole-like organ). The phyllomorph has three meristems: a basal meristem (BM; involved in lamina growth), a petiolode meristem (PM; required for midrib and petiolode growth), and a groove meristem (GM; contributes to inflorescence and new phyllomorph development). Although the GM has a tunica-corpus structure like a conventional shoot apical meristem (SAM), the vegetative GM of a one-leaf plant does not form any organ primordia and has been considered a defective or suppressed SAM. In this study, we evaluated the nature of the three meristems to reconsider their roles in phyllomorph development in the one-leaf speciesMonophyllaea glabra.


METHODS
Mitotic activities of meristem cells were monitored by incorporation of a thymidine analog (EdU) into DNA. Orthologs ofSHOOTMERISTEMLESS(STM) andPHANTASTICA,ROUGH SHEATH2,ASYMMETRIC LEAVES1(PHAN/RS2/AS1) were isolated fromM.glabra, and their expression patterns were investigated by quantitative reverse transcription polymerase chain reaction in combination with a laser microdissection technique.


RESULTS
Mitotic activities were detected in all three phyllomorph meristems. Strong expression of theSTMandPHAN/RS2/AS1orthologs was detected in the vegetative GM and BM, respectively.


CONCLUSIONS
The vegetative GM is an active meristem that expresses theSTMortholog. We postulate that the GM is required for growth of a phyllomorph by providing undifferentiated cells and/or growth regulators to the BM and/or PM.
Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Tokyo153-8902, Japan.|Graduate School of Science, The University of Tokyo, Science Building #2, 7-3-1 Hongo, Tokyo 113-0033, Japan.
Naoko
N
Ishikawa
Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan.
Hirokazu
H
Takahashi
Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan.
Mikio
M
Nakazono
Graduate School of Science, The University of Tokyo, Science Building #2, 7-3-1 Hongo, Tokyo 113-0033, Japan tsukaya@bs.s.u-tokyo.ac.jp.|Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1, Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
Hirokazu
H
Tsukaya
D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D061346:Laser Capture Microdissection; D019684:Magnoliopsida / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D018519:Meristem / Q000235:genetics / Q000254:growth & development*; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development*; D010940:Plant Proteins / Q000235:genetics; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D010940:Plant Proteins
Gesneriaceae; KNOX gene; Monophyllaea; groove meristem; indeterminate growth; phyllomorph; shoot apical meristem