Arabidopsis MICROTUBULE DESTABILIZING PROTEIN40 Is Involved in Brassinosteroid Regulation of Hypocotyl Elongation

Abstract

The brassinosteroid (BR) phytohormones play crucial roles in regulating plant cell growth and morphogenesis, particularly in hypocotyl cell elongation. The microtubule cytoskeleton is also known to participate in the regulation of hypocotyl elongation. However, it is unclear if BR regulation of hypocotyl elongation involves the microtubule cytoskeleton. In this study, we demonstrate that BRs mediate hypocotyl cell elongation by influencing the orientation and stability of cortical microtubules. Further analysis identified the previously undiscovered Arabidopsis thaliana MICROTUBULE DESTABILIZING PROTEIN40 (MDP40) as a positive regulator of hypocotyl cell elongation. BRASSINAZOLE-RESISTANT1, a key transcription factor in the BR signaling pathway, directly targets and upregulates MDP40. Overexpression of MDP40 partially rescued the shorter hypocotyl phenotype in BR-deficient mutant de-etiolated-2 seedlings. Reorientation of the cortical microtubules in the cells of MDP40 RNA interference transgenic lines was less sensitive to BR. These findings demonstrate that MDP40 is a key regulator in BR regulation of cortical microtubule reorientation and mediates hypocotyl growth. This study reveals a mechanism involving BR regulation of microtubules through MDP40 to mediate hypocotyl cell elongation.

The Microtubule Plus-End Tracking Proteins SPR1 and EB1b Interact to Maintain Polar Cell Elongation and Directional Organ Growth in Arabidopsis

“…The fact that a range of mutants altered in MT stability exhibit defects in cell growth (Ishida et al, 2007a;Perrin et al, 2007;Wang et al, 2007Wang et al, , 2012Yao et al, 2008;Li et al, 2011a) suggests that proper MT dynamics and stability may be key to proper cell expansion. Given our data showing that the cortical MT arrays in spr1-6 eb1b-2 expanding root and etiolated hypocotyl cells have relatively normal organization (Figure 4), it seems unlikely that the severe anisotropic expansion defects of these cells is due to the orientation and ordering of cortical MTs and, by extension, oriented cellulose deposition.…”

“…In other Arabidopsis mutants, alterations in MT dynamic instability parameters have been reported to correlate with defects in polar cell expansion (Ishida et al, 2007a;Yao et al, 2008;Wang et al, 2012). To determine if cortical MT dynamic instability parameters were aberrant in elongating hypocotyl cells of the spr1-6 and eb1b single and double mutants, we measured the polymerization dynamics of MT plus ends in dark-grown hypocotyl cells (upper hypocotyl, 4 d after germination) expressing EYFP:TUA5 in the wild type and spr1-6, eb1b-2, and spr1-6 eb1b-2 mutant backgrounds.…”

Rho of Plant GTPase Signaling Regulates the Behavior of Arabidopsis Kinesin-13A to Establish Secondary Cell Wall Patterns

“…Overexpression and knockdown of MAP18 or MDP40 induce hypersensitivity and resistance to microtubule depolymerizing drugs, respectively, and also induce changes in cortical microtubule arrays and abnormal cell shape (Wang et al, 2007(Wang et al, , 2012. Therefore, MAP18 and MDP40 are considered to be microtubule destabilizing proteins.…”

Environmental Nitrate Stimulates Abscisic Acid Accumulation in Arabidopsis Root Tips by Releasing It from Inactive Stores

“…The relative fluorescence intensity was quantified using ImageJ software (http://rsb.info.nih.gov/ij/; Wang et al, 2012) on an original image of a root taken directly from the confocal microscope. Fluorescence intensity was measured transversely and vertically on each root, along a 10-pixel-wide line.…”