A proteomic approach to analyzing responses of Arabidopsis thaliana root cells to different gravitational conditions using an agravitropic mutant, pin2 and its wild type

Chao Tan,Huiqiong Zheng,Hui Wang,Yue Zhang,Bin Qi,Guoxin Xu

doi:10.1186/1477-5956-9-72

Abstract

BackgroundRoot gravitropsim has been proposed to require the coordinated, redistribution of the plant signaling molecule auxin within the root meristem, but the underlying molecular mechanisms are still unknown. PIN proteins are membrane transporters that mediate the efflux of auxin from cells. The PIN2 is important for the basipetal transport of auxin in roots and plays a critical role in the transmission of gravity signals perceived in the root cap to the root elongation zone. The loss of function pin2 mutant exhibits a gravity-insensitive root growth phenotype. By comparing the proteomes of wild type and the pin2 mutant root tips under different gravitational conditions, we hope to identify proteins involved in the gravity-related signal transduction.ResultsTo identify novel proteins involved in the gravity signal transduction pathway we have carried out a comparative proteomic analysis of Arabidopsis pin2 mutant and wild type (WT) roots subjected to different gravitational conditions. These conditions included horizontal (H) and vertical (V) clinorotation, hypergravity (G) and the stationary control (S). Analysis of silver-stained two-dimensional SDS-PAGE gels revealed 28 protein spots that showed significant expression changes in altered gravity (H or G) compared to control roots (V and S). Whereas the majority of these proteins exhibited similar expression patterns in WT and pin2 roots, a significant number displayed different patterns of response between WT and pin2 roots. The latter group included 11 protein spots in the H samples and two protein spots in the G samples that exhibited an altered expression exclusively in WT but not in pin2 roots. One of these proteins was identified as annexin2, which was induced in the root cap columella cells under altered gravitational conditions.ConclusionsThe most interesting observation in this study is that distinctly different patterns of protein expression were found in WT and pin2 mutant roots subjected to altered gravity conditions. The data also demonstrate that PIN2 mutation not only affects the basipetal transport of auxin to the elongation zone, but also results in an altered expression of proteins in the root columella.

Highlights

Root gravitropsim has been proposed to require the coordinated, redistribution of the plant signaling molecule auxin within the root meristem, but the underlying molecular mechanisms are still unknown
To study the directional and magnitude effects of gravity on plants and identify the gravity-regulated proteins that function in the gravity response mechanism (Additional file 1 Figure S1), we have investigated six-day old Arabidopsis wild-type (WT) and pin2 mutant seedlings subjected to one of the following four treatments: (1) clinorotation at 5 rpm for 12 h along their horizontal axis in a horizontal clinostat (H, simulated weightlessness); (2) clinorotation at 5 rpm for 12 h along the vertical axis in a vertical clinostat (V, clinostat control); (3) centrifugation for 30 min in a low-speed centrifuge to impose hypergravity (7 g)(G); (4) a stationary, control environment(S, ground gravitational force)
To gain further insight into the molecular basis of these different responses to altered gravity, we have compared the proteomes of Arabidopsis wild type (WT) and pin2 mutant root tips subjected to horizontal clinorotation or hypergravity with those of V and S-treated roots

Summary

Introduction

Root gravitropsim has been proposed to require the coordinated, redistribution of the plant signaling molecule auxin within the root meristem, but the underlying molecular mechanisms are still unknown. PIN proteins are membrane transporters that mediate the efflux of auxin from cells. The PIN2 is important for the basipetal transport of auxin in roots and plays a critical role in the transmission of gravity signals perceived in the root cap to the root elongation zone. By comparing the proteomes of wild type and the pin mutant root tips under different gravitational conditions, we hope to identify proteins involved in the gravity-related signal transduction. Transport of auxin across the plasma membrane is mediated by two types of influx carriers (AUXIN1/like Aux family) and efflux (PIN-FORMED family) carriers [13,14,15,16,17,18,19,20]. The polar subcellular localization of these PIN proteins in the plasma membrane determines the direction of intercellular auxin flow and thereby the gravitropic growth response [26]

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