Space–time analysis of gravitropism in etiolated Arabidopsis hypocotyls using bioluminescence imaging of the IAA19 promoter fusion with a destabilized luciferase reporter

Abstract

Imaging analysis was carried out during the gravitropic response of etiolated Arabidopsis hypocotyls, using an IAA19 promoter fusion of destabilized luciferase as a probe. From the bright-field images we obtained the local deflection angle to the vertical, A, local curvature, C, and the partial derivative of C with respect to time, . These were determined every 19.9 µm along the curvilinear length of the hypocotyl, at ~10 min intervals over a period of ~6 h after turning hypocotyls through 90° to the horizontal. Similarly from the luminescence images we measured the luminescence intensity of the convex and concave flanks of the hypocotyl as well as along the median of the hypocotyl, to determine differential expression of auxin-inducible IAA19. Comparison of these parameters as a function of time and curvilinear length shows that the gravitropic response is composed of three successive elements: the first and second curving responses and a decurving response (autostraightening). The maximum of the first curving response occurs when A is 76° along the entire length of the hypocotyl, suggesting that A is the sole determinant in this response; in contrast, the decurving response is a function of both A and C, as predicted by the newly-proposed graviproprioception model (Bastien et al., Proc Natl Acad Sci USA 110:755–760, 2013). Further, differential expression of IAA19, with higher expression in the convex flank, is observed at A = 44°, and follows the Sachs’ sine law. This also suggests that IAA19 is not involved in the first curving response. In summary, the gravitropic response of Arabidopsis hypocotyls consists of multiple elements that are each determined by separate principles.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-017-0932-6) contains supplementary material, which is available to authorized users.

The exogenous application of the apocarotenoid retinaldehyde negatively regulates auxin-mediated root growth

“…S8). An auxin-inducible pIAA19::ELucPEST reporter (Yamamoto et al, 2017) was used for quantifying auxin signaling. IAA19 activity increased two-fold in the root tip area following treatment with 10 nM 1-naphthaleneacetic acid (NAA), a synthetic auxin.…”

Growth-mediated plant movements: hidden in plain sight

“…How are proprioceptive cues sensed and transduced into differential growth? Studies using radiolabeled auxin or examining expression of an auxin-responsive reporter gene suggest that autostraightening does not depend upon lateral redistribution of auxin [41,42]. Instead, local curvature appears to be sensed via an actinomyosin-dependent mechanism that triggers autostraightening via an unknown mechanism.…”

2018 Awards in the Journal of Plant Research

“…Kotaro T. Yamamoto, Masaaki K. Watahiki, Jun Matsuzaki, and Soichirou Satoh in the Faculty of Science at Hokkaido University and Hisayo Shimizu in the Graduate School of Life Science at Hokkaido University studied gravitropic response, which is one of the most fundamental growth responses in plants (Yamamoto et al 2017). They conducted an imaging analysis of the gravitropic response of etiolated Arabidopsis hypocotyls, using an IAA19 promoter fusion of destabilized luciferase as a probe.…”

“…The Botanical Society of Japan sponsored the conversion of seven papers originally published without open access to open access in 2018. Two of those are awardees of the best paper award mentioned in the section above (Takemura et al 2017;Yamamoto et al 2017). Five papers are reviews published in the category of "Current Topics in Plant Research" (Inada 2017;Inoue et al 2018;Kobayashi 2016;Kotake et al 2016;Kume 2017).…”