A Bird’s-Eye View of Molecular Changes in Plant Gravitropism Using Omics Techniques

Abstract

During evolution, plants have developed mechanisms to adapt to a variety of environmental stresses, including drought, high salinity, changes in carbon dioxide levels and pathogens. Central signaling hubs and pathways that are regulated in response to these stimuli have been identified. In contrast to these well studied environmental stimuli, changes in transcript, protein and metabolite levels in response to a gravitational stimulus are less well understood. Amyloplasts, localized in statocytes of the root tip, in mesophyll cells of coleoptiles and in the elongation zone of the growing internodes comprise statoliths in higher plants. Deviations of the statocytes with respect to the earthly gravity vector lead to a displacement of statoliths relative to the cell due to their inertia and thus to gravity perception. Downstream signaling events, including the conversion from the biophysical signal of sedimentation of distinct heavy mass to a biochemical signal, however, remain elusive. More recently, technical advances, including clinostats, drop towers, parabolic flights, satellites, and the International Space Station, allowed researchers to study the effect of altered gravity conditions -real and simulated micro-as well as hypergravity on plants. This allows for a unique opportunity to study plant responses to a purely anthropogenic stress for which no evolutionary program exists. Furthermore, the requirement for plants as food and oxygen sources during prolonged manned space explorations led to an increased interest in the identification of genes involved in the adaptation of plants to microgravity. Transcriptomic, proteomic, phosphoproteomic, and metabolomic profiling strategies provide a sensitive high-throughput approach to identify biochemical alterations in response to changes with respect to the influence of the gravitational vector and thus the acting gravitational force on the transcript, protein and metabolite level. This review aims at summarizing recent experimental approaches and discusses major observations.

Genetic dissection of the Arabidopsis spaceflight transcriptome: Are some responses dispensable for the physiological adaptation of plants to spaceflight?

“…Plants in spaceflight differentially express genes compared to their ground controls, suggesting that physiological adaptation is taking place in plants on orbit. There have now been a number of transcriptomic and proteomic comparisons of Arabidopsis and other plants grown in spaceflight environments [ 19 , 23 , 38 , 46 – 57 ] and the topic of plant growth in space has been recently reviewed [ 58 – 63 ]. In addition, there is more to growing in an orbital environment than the simple removal of gravity.…”

A member of the CONSTANS-Like protein family is a putative regulator of reactive oxygen species homeostasis and spaceflight physiological adaptation

“…In a recent review, it has been suggested that altered ROS signalling in response to the spaceflight environment could affect plant growth and development indirectly via changes in hormonal influx within the plants (Schüler et al 2015). OMG1 was found to regulate the expression of ROS-associated genes GRX480 and MYB77 .…”

“…The physiological impact of spaceflight is reflected in the patterns of gene expression. Irrespective of plant growth hardware, duration in space or age of plants, one consensus is that spaceflight elicits responses from pathways associated with cell wall remodelling, cell polarity, phytohormone-mediated processes, as well as general stress responses, such as wounding, pathogen defence, heat shock and reactive oxygen species (ROS) (Joo et al 2001; Paul et al 2005, 2012b, 2013a; Correll et al 2013; Zupanska et al 2013; Ferl et al 2014; Mazars et al 2014; Sugimoto et al 2014; Zhang et al 2014; Kwon et al 2015; Schüler et al 2015). In addition, a large proportion of genes differentially expressed in spaceflight encode unknown proteins.…”

A Core Regulatory Pathway Controlling Rice Tiller Angle Mediated by the LAZY1-Dependent Asymmetric Distribution of Auxin

“…Genetic studies in Arabidopsis have identified several genes involved in shoot gravitropism such as SGR genes and PHOSPHOGLUCOMUTASE genes (Hashiguchi et al, 2013(Hashiguchi et al, , 2014Kim et al, 2016;Kolesnikov et al, 2016). Although other studies have used "omics" techniques and identified gravitropism-related genes or proteins in several species (Moseyko et al, 2002;Kimbrough et al, 2004;Hu et al, 2013Hu et al, , 2015Schenck et al, 2013;Taniguchi et al, 2014;Gerttula et al, 2015;Schüler et al, 2015), the direct link between tiller or branch angle and gravitropism has not yet been established.…”