IbMADS1 (Ipomoea batatas MADS-box 1 gene) is involved in tuberous root initiation in sweet potato (Ipomoea batatas).
OBJECTIVE
The tuberization mechanism of sweet potato (Ipomoea batatas) has long been studied using various approaches. Morphological data have revealed that the tuberizing events result from the activation of the cambium, followed by cell proliferation. However, uncertainties still remain regarding the regulators participating in this signal-transduction pathway. An attempt was made to characterize the role of one MADS-box transcription factor, which was preferentially expressed in sweet potato roots at the early tuberization stage.


METHODS
A differential expression level of IbMADS1 (Ipomoea batatas MADS-box 1) was detected temporally and spatially in sweet potato tissues. IbMADS1 responses to tuberization-related hormones were assessed. In order to identify the evolutionary significance, the expression pattern of IbMADS1 was surveyed in two tuber-deficient Ipomoea relatives, I. leucantha and I. trifida, and compared with sweet potato. In functional analyses, potato (Solanum tuberosum) was employed as a heterologous model. The resulting tuber morphogenesis was examined anatomically in order to address the physiological function of IbMADS1, which should act similarly in sweet potato.


RESULTS
IbMADS1 was preferentially expressed as tuberous root development proceeded. Its expression was inducible by tuberization-related hormones, such as jasmonic acid and cytokinins. In situ hybridization data showed that IbMADS1 transcripts were specifically distributed around immature meristematic cells within the stele and lateral root primordia. Inter-species examination indicated that IbMADS1 expression was relatively active in sweet potato roots, but undetectable in tuber-deficient Ipomoea species. IbMADS1-transformed potatoes exhibited tuber morphogenesis in the fibrous roots. The partial swellings along fibrous roots were mainly due to anomalous proliferation and differentiation in the xylem.


CONCLUSIONS
Based on this study, it is proposed that IbMADS1 is an important integrator at the initiation of tuberization. As a result, the initiation and development of tuberous roots seems to be well regulated by a network involving a MADS-box gene in which such hormones as jasmonic acid and cytokinins may act as trigger factors.
Ku
Amy Tsu
AT
Institute of Plant Biology, National Taiwan University, 10617, Taipei, Taiwan.
Huang
Yi-Shiuan
YS
Wang
Yu-Shu
YS
Ma
Daifu
D
Yeh
Kai-Wun
KW
D000040:Abscisic Acid / Q000494:pharmacology; D054458:Amplified Fragment Length Polymorphism Analysis; D003517:Cyclopentanes / Q000494:pharmacology; D003583:Cytokinins / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017403:In Situ Hybridization; D027723:Ipomoea batatas / Q000235:genetics* / Q000254:growth & development; D026161:MADS Domain Proteins / Q000235:genetics* / Q000302:isolation & purification; D054883:Oxylipins / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics* / Q000302:isolation & purification; D018517:Plant Roots / Q000235:genetics* / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development; D020133:Reverse Transcriptase Polymerase Chain Reaction
D003517:Cyclopentanes; D003583:Cytokinins; D026161:MADS Domain Proteins; D054883:Oxylipins; D010940:Plant Proteins; C011006:jasmonic acid; D000040:Abscisic Acid