Poster: Hormones

Abs # 618: Auxin and ethylene response interactions during Arabidopsis root hair development dissected by auxin influx modulators

Presenter:	Rahman, Abidur , abidur@popx.tokai.jaeri.go.jp
Authors	Rahman, Abidur  (A) (B)  Hosokawa, Satoko  (C)   Oono, Yutaka  (A)   Amakawa, Taisaku  (B)   Goto, Nobuharu  (E)   Tsurumi, Seiji  (D)
Affiliations:	(A): Japan Atomic Energy Research Institute (B): Graduate School of Science and Technology,Kobe University (C): Faculty of Science, Kobe University (D): Radio Isotope Research Center, Kobe University (E): Department of Biology, Miyagi University of Education

The plant hormones auxin and ethylene have been shown to play important roles during root hair development. However, cross-talk between auxin and ethylene makes it difficult to understand the independent role of either hormone. To dissect their respective roles we examined the effects of two compounds, chromosaponin I (CSI) and 1-naphthoxyacetic acid (1-NOA), on the root hair developmental process in wild-type Arabidopsis thaliana, ethylene insensitive mutant ein2-1, auxin influx mutants aux1-7, aux1-22 and double mutant aux1-7 ein2. GUS expression analysis in the BA-GUS transgenic line, consisting of auxin responsive domains of PS-IAA4/5 promoter and b-glucuronidase (GUS) reporter, revealed that 1-NOA and CSI act as auxin uptake inhibitors in Arabidopsis roots. The frequency of root hairs in ein2-1 roots was greatly reduced in the presence of CSI or 1-NOA, suggesting that endogenous auxin plays a critical role for the root hair initiation in the absence of an ethylene response. All these mutants showed a reduction in root hair length, however, the root hair length could be restored with a variable concentration of 1-naphthaleneacetic acid (NAA). 10 nM NAA restored the root hair length of aux1 mutants to wild-type level, while 100 nM NAA was needed for ein2-1 and aux1-7 ein2 mutants. Our results suggest that insensitivity in ethylene response affects the auxin-driven root hair elongation. CSI exhibited a similar effect to 1-NOA, reducing root hair growth and the number of root hair bearing cells in wild-type and ein2-1 roots, while stimulating these traits in aux1-7and aux1-7ein2 roots, confirming that CSI is a unique modulator of AUX1.