Journal
PLANT PHYSIOLOGY
Volume 178, Issue 3, Pages 1370-1389Publisher
AMER SOC PLANT BIOLOGISTS
DOI: 10.1104/pp.18.00126
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Funding
- Baen-dWurttemberg Stiftung
- Bundesministerium fur Bildung und Forschung (BMBF SYSBRA, SYSTEC, Microsystems)
- Excellence Initiative of the German Federal and State Governments [EXC 294]
- Deutsche Forschungsgemeinschaft [DFG SFB 746, INST 39/839,840,841]
- Deutsches Zentrum fur Luft und Raumfahrt [DLR 50WB1022]
- Deutscher Akademischer Austauschdienst (DAAD)
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Plants respond to gravitational force through directional growth along the gravity vector. Although auxin is the central component of the root graviresponse, it works in concert with other plant hormones. Here, we show that the folate precursor para-aminobenzoic acid (PABA) is a key modulator of the auxin-ethylene interplay during root gravitropism in Arabidopsis (Arabidopsis thaliana). In gravistimulated roots, PABA promotes an asymmetric auxin response, which causes the asymmetric growth responsible for root curvature. This activity requires the auxin response transcription factors AUXIN RESPONSE FACTOR7 (ARF7) and ARF19 as well as ethylene biosynthesis and signaling, indicating that PABA activity requires both auxin and ethylene pathways. Similar to ethylene, exogenous PABA reverses the agravitropic root growth of the auxin transport mutant pin-formed2 (pin2) and the auxin biosynthetic double mutant with loss of function of weak ethylene insensitive (wei) genes, wei8wei2, but not the pin2wei8wei2 triple mutant. This finding suggests that PABA regulates the ethylene-dependent reciprocal compensation between auxin transport and biosynthesis. Furthermore, manipulation of endogenous free PABA levels by modulating the expression of the gene encoding its glucosylation enzyme, UDP-GLYCOSYL TRANSFERASE75B1, impacts the root graviresponse, suggesting that endogenous free PABA levels may play a crucial role in modulating the auxin-ethylene cross talk necessary for root gravitropism.
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