Presentation Information
[MS15-03]A mutual inhibition between phytohormone auxin and EPFL peptides modulates the periodic pattern of auxin in model plant Arabidospsis
*Toshiaki Tameshige1,2, Takeshi Tsuchida2, Yuuki Matsushita3,4, Koichi Fujimoto3, Momoko Ikeuchi2 (1. Kyoto Pref. Univ. (Japan), 2. NAIST (Japan), 3. Hiroshima Univ. (Japan), 4. NCBS (India))
Keywords:
reaction-diffusion system,bistability,leaf morphology,auxin
Periodic patterns are lying under many multicellular morphogenesis in animals and plants. Plants repetitively develop leaves and the serrations (jagged leaf margins) through their lives. Development of leaves and serrations largely depend on the phytohormone auxin which is periodically accumulated via polar auxin transport in the tissues. The concentrated auxin triggers local cellular auxin response, or “auxin response maximum”, which serves as the positional cue for new leaf formation in the shoot apical meristem and new serration along leaf margin. It has been known that the auxin transporter PIN-FORMED1 (PIN1) determines the auxin transport polarity of each cell so that the auxin flow occurs toward the cell with the highest auxin response among the neighboring cells. It has been well documented that this auxin-PIN1 feedback system, so-called up-the-gradient auxin transport, autonomously forms auxin response maxima in a periodic manner from experimental and theoretical studies. However, it remains unresolved what regulates the actual interval length between the maxima. EPIDERMAL PATTERNING FACTOR-LIKE 2 (EPFL2), a secreted peptide, and auxin form another feedback circuit in which they mutually repress each other, and the spatial patterns of auxin response and EPFL2 expression are mutually exclusive. It has been elusive whether EPFL2 has any effect on the spacing of auxin maxima formation.
In this study, we performed molecular genetic experiments in Arabidopsis and mathematical modeling in order to reveal the function of EPFL2 in auxin pattern. In our model, the relationship between auxin and EPFL2 is implemented as a bistable system, and combined with a known simple model of up-the-gradient polar auxin transport system. First, epfl2 mutant lacking EPFL2, was observed. The interval of the auxin response maxima along leaf margin was shorter than that in the wild type. Such shorter intervals were recapitulated in the model simulation by partly decreasing the parameter of the EPFL2 synthesis rate mimicking the mutant. However, when this parameter is set close to zero, the peak shape of the auxin response becomes broader. This was not so obviously seen in the epfl2 mutant, suggesting the existence of another gene with redundant function with EPFL2. Next, we observed epfl1 epfl2 double mutants that is also lacking EPFL1, the gene most similar to EPFL2, and found that the broad peak predicted by the model was indeed observed. In this presentation, we will discuss how a mutual inhibitory gene regulation affects the periodic pattern of a diffusion-driven patterning system.
In this study, we performed molecular genetic experiments in Arabidopsis and mathematical modeling in order to reveal the function of EPFL2 in auxin pattern. In our model, the relationship between auxin and EPFL2 is implemented as a bistable system, and combined with a known simple model of up-the-gradient polar auxin transport system. First, epfl2 mutant lacking EPFL2, was observed. The interval of the auxin response maxima along leaf margin was shorter than that in the wild type. Such shorter intervals were recapitulated in the model simulation by partly decreasing the parameter of the EPFL2 synthesis rate mimicking the mutant. However, when this parameter is set close to zero, the peak shape of the auxin response becomes broader. This was not so obviously seen in the epfl2 mutant, suggesting the existence of another gene with redundant function with EPFL2. Next, we observed epfl1 epfl2 double mutants that is also lacking EPFL1, the gene most similar to EPFL2, and found that the broad peak predicted by the model was indeed observed. In this presentation, we will discuss how a mutual inhibitory gene regulation affects the periodic pattern of a diffusion-driven patterning system.