An ABC transporter B family protein, ABCB19, is required for cytoplasmic streaming and gravitropism of the inflorescence stems.
A significant feature of plant cells is the extensive motility of organelles and the cytosol, which was originally defined as cytoplasmic streaming. We suggested previously that a three-way interaction between plant-specific motor proteins myosin XIs, actin filaments, and the endoplasmic reticulum (ER) was responsible for cytoplasmic streaming. (1) Currently, however, there are no reports of molecular components for cytoplasmic streaming other than the actin-myosin-cytoskeleton and ER-related proteins. In the present study, we found that elongated cells of inflorescence stems of Arabidopsis thaliana exhibit vigorous cytoplasmic streaming. Statistical analysis showed that the maximal velocity of plastid movements is 7.26 µm/s, which is much faster than the previously reported velocities of organelles. Surprisingly, the maximal velocity of streaming in the inflorescence stem cells was significantly reduced to 1.11 µm/s in an Arabidopsis mutant, abcb19-101, which lacks ATP BINDING CASSETTE SUBFAMILY B19 (ABCB19) that mediates the polar transport of the phytohormone auxin together with PIN-FORMED (PIN) proteins. Polar auxin transport establishes the auxin concentration gradient essential for plant development and tropisms. Deficiency of ABCB19 activity eventually caused enhanced gravitropic responses of the inflorescence stems and abnormally flexed inflorescence stems. These results suggest that ABCB19-mediated auxin transport plays a role not only in tropism regulation, but also in cytoplasmic streaming.
a Graduate School of Science, Kyoto University , Kyoto 606-8502 , Japan.|d These authors contributed equally to this work.
Keishi
K
Okamoto
a Graduate School of Science, Kyoto University , Kyoto 606-8502 , Japan.|d These authors contributed equally to this work.
Haruko
H
Ueda
a Graduate School of Science, Kyoto University , Kyoto 606-8502 , Japan.
Tomoo
T
Shimada
a Graduate School of Science, Kyoto University , Kyoto 606-8502 , Japan.
Kentaro
K
Tamura
a Graduate School of Science, Kyoto University , Kyoto 606-8502 , Japan.
Yasuko
Y
Koumoto
b Graduate School of Biological Sciences, Nara Institute of Science and Technology , Ikoma 630-0101 , Japan.
Masao
M
Tasaka
b Graduate School of Biological Sciences, Nara Institute of Science and Technology , Ikoma 630-0101 , Japan.|c Current address: Graduate School of Bioagricultural Sciences, Nagoya University , Nagoya 464-8601 , Japan.
Miyo Terao
MT
Morita
a Graduate School of Science, Kyoto University , Kyoto 606-8502 , Japan.
Ikuko
I
Hara-Nishimura
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003595:Cytoplasmic Streaming / Q000235:genetics*; D018522:Gravitropism / Q000235:genetics*; D007210:Indoleacetic Acids / Q000378:metabolism; D009154:Mutation; D018547:Plant Stems / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction
C532604:ABCB19 protein, Arabidopsis; D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids
ABC transporter; ABCB19; Arabidopsis thaliana, cytoplasmic streaming; MDR1; PGP19; shoot gravitropism