Roles of MAP65-1 and BPP1 in Gravity Resistance of Arabidopsis hypocotyls

Abstract

The present experiment aims to clarify the roles of 65 kDa microtubule-associated protein-1 (MAP65-1) and basic proline-rich protein1 (BPP1), which are involved in the maintenance of transverse microtubule orientation, in gravity resistance, using green fluorescent protein (GFP)-expressing Arabidopsis lines. Hypergravity at 300 G inhibited elongation growth and promoted lateral expansion of epidermal cells in the subapical region of hypocotyls in GFP-MAP65-1 line expressing by native promoter and BPP1-GFP line expressing by a constitutive cauliflower mosaic virus 35S promoter. In BPP1-GFP line, hypergravity showed smaller effects on modification of growth anisotropy than wild type. Also, hypergravity induced reorientation of cortical microtubules from transverse to longitudinal directions in both lines. However, in BPP1-GFP line, hypergravity showed smaller effects on reorientation of cortical microtubules. When the expression levels of MAP65-1 were determined by analyzing GFP fluorescence in hypocotyls of GFP-MAP65-1 line, hypergravity decreased the levels of MAP65-1 in the subapical region, where hypergravity modified growth anisotropy and orientation of cortical microtubules. These results indicate that the regulation of levels of MAP65-1 and BPP1 is involved in the hypergravity-induced reorientation of cortical microtubules, which may lead to modification of growth anisotropy, thereby developing a tough body against the gravitational force in Arabidopsis hypocotyls

Dynamics of Actin Filaments in Epidermal Cells of Azuki Bean Epicotyls under Hypergravity Conditions

“…We reported previously that hypergravity clearly promoted lateral expansion in the apical region of azuki bean epicotyls (Nakano et al, 2007). Also, hypergravity-induced modification of the growth anisotropy mainly occurred in upper region of Arabidopsis hypocotyls (Murakami et al, 2016). These results indicate that the upper regions have larger capacity to modify the growth anisotropy in response to the changes in the magnitude of gravity.…”

“…On the other hand, in the presence of cytochalasin D, frequency of cells having longitudinal, oblique, or transverse was almost the same in epicotyls grown at 1 G. Furthermore, hypergravity did not induce reorientation of cortical microtubules in the presence of cytochalasin D. Thus, the distribution pattern of four types of cells was identical between 1 G and 300 G conditions. We have reported that the hypergravity-induced modification of growth anisotropy may be mediated by reorientation of cortical microtubules from transverse to longitudinal directions in azuki bean epicotyls and Arabidopsis hypocotyls (Matsumoto et al, 2010;Murakami et al, 2016). Also, Sampathkumar et al (2011) showed that the modification of dynamics of actin filaments may be associated with orientation of cortical microtubules in Arabidopsis hypocotyls.…”

“…We have shown that the gravitational force affected the orientation of cortical microtubules during modification of anisotropic growth of stems. Hypergravity, which inhibited elongation growth and promoted lateral growth in shoots, increased cortical microtubules with longitudinal orientation, but decreased those with transverse orientation in azuki bean epicotyls and Arabidopsis hypocotyls (Matsumoto et al, 2010;Murakami et al, 2016). On the other hand, microgravity, which promoted elongation growth and inhibited lateral growth in shoots, decreased cortical microtubules with longitudinal orientation, but increased those with transverse orientation in Arabidopsis hypocotyls (Soga et al, 2018a).…”

Centrifugal displacement of nuclei in epidermal cells of azuki bean epicotyls

“…Centrifugal hypergravity, the gravitational acceleration of more than 1 G, has been utilized for gravitational biology experiments. Various plants have been grown under hypergravity conditions, and shown to develope a short and thick body (Hoson and Soga, 2003;Wakabayashi et al, 2005;Nakano et al, 2007;Murakami et al, 2016). Based on the results of hypergravity experiments, it was hypothesized that plant body would become longer and thinner under microgravity conditions in space.…”

“…The shape of the plant body depends generally on the shape of its individual cells, which is primarily controlled by the orientation of cortical microtubules (Shibaoka, 1994). Hypergravity, which stimulated the development of a short and thick body, induced reorientation of cortical microtubules from transverse to longitudinal directions in epidermal cells of azuki bean epicotyls (Soga et al, 2006) and Arabidopsis hypocotyls (Matsumoto et al, 2010;Murakami et al, 2016). On the other hand, microgravity, which stimulated the development of a longer and thinner body, induced reorientation of cortical microtubules from longitudinal to transverse directions in epidermal cells of Arabidopsis hypocotyls (Soga et al, 2018a).…”