1. Auxin moves from the pericycle cells towards the outer tissues.
Auxin moves from the pericycle cells towards the outer tissues. (A–L) Tissue‐specific expression of the Agrobacterium indole‐3‐acetamide hydrolase (iaaH) gene was used as a tool to control auxin synthesis. Expression of the iaaH gene under the control of the J0121 GAL4 driver line (B) resulted in production of numerous lateral roots upon 1 μM indole‐3‐acetamide treatment whereas wild‐type plants (Col‐0) were not affected (A). Transgenic Arabidopsis plants were engineered to synthesise IAA in xylem‐pole pericycle (XPP) cells using the XPP‐specific GAL4 drive line, J0121 (C) by targeting the expression of the bacterial iaaH enzyme fused to the RFP tag (D). Therefore, the J0121 and iaaH fluorescent markers (respectively GFP and RFP) are co‐expressed in the XPP tissue (E). Plant roots were fed with 5 μM deuterated indole‐3‐acetamide (D5‐IAM), and the ratio of D5‐IAA to IAA was determined by mass spectrometry analysis. A strong D5‐IAA signal was detected upon 10 and 20 h after incubation in the J0121>>iaaH‐RFP line, whereas very little D5‐IAA was detected in the control (J0121) line even after 20 h of incubation (F). As a result of auxin synthesis in the xylem‐pole pericycle cells, we observed an overexpression of LAX3 (G) and PG (H). The J0121 line is specifically expressed in three pericycle cell files associated with each of the xylem poles as seen with the GFP reporter (I) and as reported previously (Laplaze et al, 2005). (J–L) We monitored the effect of auxin synthesis in the pericycle on the LAX3 expression pattern by crossing the J0121>>iaaH‐RFP plants with the pLAX3:LAX3YFP‐expressing plants and subsequent analysis on the F1 progeny. LAX3‐YFP accumulation was visualised upon 18 h treatment with mock (J), 1 μM IAM (K) or 10μM IAM (L). Note that strong expression of LAX3 in the vasculature is seen as in the non‐treated control. Bars are 25 μm (I–L), 50 μm (C–E) and 5 mm (A, B). Data shown are mean value±s.e.m. and n=100 plants. Asterisks indicate a significant difference with corresponding control experiment by Student's t‐test (*P<0.05; **P<0.01; ***P<0.001).
Benjamin Péret et al. Mol Syst Biol 2013;9:699
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