75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

397 A GPI-Anchored Protein Regulates Stimulus-Induced Root Hair Elongation
Yoshihiro Koshino-Kimura 1 , Haruna Kiriyama 1 , Akira Yoshimori 1 , Miyuki Kubo 1 , Takuji Wada 2 , Taisuke Nishimura 3 ,
Mayumi Ohta 1 , Sumie Ishiguro 4 , Ryuji Tsugeki 1 , Noritaka Matsumoto 1 , Kiyotaka Okada 1
1
Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, 2 Plant Science Center, RIKEN,
Yokohama 230-0045, Japan, 3 Laboratory of Plant Genetics, University of Geneva, Geneva, Switzerland,
4
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
To uptake water and nutrients efficiently, plants have many root hairs on their roots. In order to fulfill their function,
roots and root hairs should touch soil. Length and direction of Arabidopsis root hairs are changed depending on touch
or untouch of the root tip to agar surface. When roots are grown on agar surface, root hairs are perpendicular to the root
surface, however, when roots come apart from the agar, hairs get longer and tilted to the root tip. To clarify the molecular
mechanism of this response, we isolated mutants defective in this response. Root hairs of timid (tmd) mutant are shorter
on agar than those of wild type, and become still much shorter when the root does not touch agar. The direction of the
root hairs in tmd were, however, normally changed when the root came off the agar surface. Map-based cloning revealed
that the TMD gene encodes a putative GPI-anchored protein. The TMD gene began to be expressed in hair-forming cells
just before the root-hair bulge were observed. The TMD protein was shown to be localized in plasma membranes and
endosomes. Possible function of TMD protein in the elongation of root hairs in response to the environment will be
discussed.
398 Isolation and Characterization of SOR12, a Novel Regulator of Cytokinin-Mediated Leaf
Senescence
In Chul Lee, Hyo Jung Kim, Tae Hoon Kim, Seung Hee Choi, Hong Gil Nam
Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang, Kyungbuk,
790-784, Korea
Senescence is a sequence of biochemical and physiological events that constitute the final stage of development.
Senescence is now clearly regarded as a genetically programmed and evolutionally acquired developmental process.
However, in spite of the biological and practical importance, genetic mechanism of senescence has been very limited.
Previously, we reported that ore12-1 has increased leaf longevity due to a missense mutation in AHK3, a sensor
histidine kinase cytokinin receptor, and suggested that cytokinins exert their anti-senescing effect specifically and
positively through AHK3 to control senescence (Kim et al., 2006). To identify signaling components downstream of
AHK3, we have undertaken a systematic genetic screening in an ore12-1 allele through ethyl methanesulfonate (EMS)-
mutagenesis. One suppressor named sor12 (suppressor of ore12-1) was identified and showed complete suppression of
the ore12-1 senescence phenotypes. sor12 ore12-1 double mutants exhibited accelerated senescence symptoms in agedependent
leaf senescence as well as in dark-induced senescence. Furthermore, sor12 ore12-1 dramatically reduced the
sensitivity of the plant to cytokinins in delaying leaf senescence and in inducing cytokinin-responsive genes, although
these mutants still showed normal sensitivity to cytokinins in other responses, such as shoot induction and hypocotyl
elongation inhibition.
Therefore, we suggest that SOR12 plays a major role in controlling cytokinin-mediated leaf senescence as a
downstream component of AHK3. The identification of the mutated genes is underway and will be reported soon.