The Transcript Level of Katanin Gene is Increased Transiently in Response to Changes in Gravitational Conditions in Azuki Bean Epicotyls

Abstract

Development of a short and thick body by re orie ntation of cor tical microtubule s is required for the resistance of plants to the gravitational force. Katanin has microtubules e ve r i n g a c t i v i t y a n d i s i nvo l ve d i n t h e reorientation of cortical microtubules. Here, we investigated the effects of hypergravity produced by centrifugation on the expression of VaKTN1 gene encoding katanin. Hypergravity at 300 G increased the transcript level within 15 min, and the level reached maximum at 45 min. Then, the level was decreased and returned to the control range at 2 h. Also, the expression of VaKTN1 gene was increased transiently by removal of hypergravity stimulus. Changes in the microtubule-severing activity as a result of the modification of VaKTN1 expression in response to changes in gravitational conditions may b e involve d in the re gulation of the orientation of cortical microtubules, leading to changes in the shape of plant body. Lanthanum and gadolinium ions, potential blockers of mechanosensitive calcium ion-permeable channels (mechanoreceptors), nullified the up-regulation of VaKTN1 gene, suggesting that mechanoreceptors are responsible for regulation by gravity of VaKTN1 expression.

Cortical microtubules are responsible for gravity resistance in plants

“…19,20 In our recent study, we found that gadolinium ions decreased the alignment angle of epidermal cell files and that of cortical region of azuki bean epicotyls, cells with transverse cortical microtubules were predominant at 1 g. Hypergravity induces reorientation of cortical microtubules from transverse to longitudinal directions. 9 In addition, hypergravity increased transiently the expression of γ-tubulin and katanin genes, 10,11 which are assumed to be responsible for reorientation of cortical microtubules. 12 These results suggest that cortical microtubules are involved in gravity resistance.…”

Transient increase in the levels of γ-tubulin complex and katanin are responsible for reorientation by ethylene and hypergravity of cortical microtubules

“…When expression profiles of katanin gene were compared with those of g-tubulin complex genes, the peak of expression of katanin gene was delayed by 1.0 to 1.5 h. The delay of the peak of expression of katanin gene was also observed during hypergravity-induced reorientation of cortical microtubules from transverse to longitudinal directions. 10,11 These results indicate that microtubule-severing activities are increased by ethylene and hypergravity via upregulation of katanin gene, resulting in the stimulation of separation of the newly synthesized microtubule branch via g-tubulin complex (Fig. 1).…”

“…2 By removal of the hypergravity stimulus, the transcript levels of g-tubulin complex and katanin genes were increased transiently. 10,11 These results indicate the transcription of g-tubulin complex and katanin genes is stimulated transiently during reorientation of cortical microtubules, irrespective of the direction of reorientation of the microtubules.…”

Growth and Morphogenesis of Azuki Bean Seedlings in Space during SSAF2013 Program

“…As the final step of gravity resistance, plants developed a short and thick body and increased cell wall rigidity to resist the gravitational force. The modification of body shape was brought about by the rapid reorientation of cortical microtubules that was caused by the action of microtubule-associated proteins in response to the magnitude of the gravitational force (Soga et al, , 2009. The regulation of the cell wall rigidity was brought about by modification of the metabolisms of antigravitational cell wall polysaccharides (Hoson and Soga, 2003;Nakano et al, 2007).…”