Morphological and gene expression pattern changes in wrky46 mutant arabidopsis thaliana under altered gravity conditions

Arabidopsis roots are important organs for gravity sensing and gravitropic response. Long-term exposure of Arabidopsis to three-dimensional (3D) clinorotation was found to result in increased expression of WRKY46. In this study, the response of wrky46 mutants, constructed by T-DNA insertion, to simulated microgravity and gravistimulation by reorientation was studied. Microgravity conditions were simulated using a 3D clinostat, which simulates weightlessness. Morphological changes, such as root coiling, waving, and multidirectional growth patterns, were observed in the wild type (WT) seedlings after only 4 days of 3D clinorotation treatment, while in the wrky46 mutant seedlings, the changes observed were minimal compared with those of WT seedlings. Polar auxin transport played an important role in the observed morphological changes. Therefore, expression of the polar auxin transport genes AUX1, PIN2, -3, -4, and -7, and ARG1 was analyzed. Their expression was found to be higher in wrky46 seedlings than in WT seedlings under 3D clinorotation. Gravistimulation by reorientation was achieved by horizontally reorienting the seedlings. Root tip bending to 90° was observed in all WT seedlings within 18–20 h, whereas in mutant seedlings, bending of the root tip to a right angle took more than 20 h. AXR expression is known to directly correlate with root tip bending. The expression of AXR1, -2, -3, -4 was found to be higher in WT seedlings relative to mutant seedlings under gravistimulation by reorientation. However, their expression was relatively low in both WT and wrky46 plants under 3D clinorotation. These results suggest that WRKY46 plays an important role in the root gravitropic response, and in the reduction of polar auxin transport that is necessary for decreasing the effect of gravity due to clinorotation.