Proteome analysis of apical and basal regions of poplar stems under gravitropic stimulation

Abstract

Gravity is a constant force guiding the direction of plant growth. In young poplar stem, reorientation of the apical region is mainly obtained by differential growth of elongating primary tissues. At the base, where elongation is achieved but where the cambium is active, reorientation is due to asymmetrical formation of reaction wood. After 45 min of gravistimulation, the stem showed no reorientation, but 1 week later, reaction wood was observed at the base of the stem. To determine the molecular mechanisms taking place at the top and base of the stem, after 45 min or 1 week of inclination, the changes induced in protein accumulation were studied by two-dimensional polyacrylamide gel electrophoresis and quantitatively analyzed using image analysis software. Around 300 protein spots were reproducibly detected and analyzed. Forty percent of these proteins showed significant changes after inclination. Mass spectrometry analysis of 135 spots led to the identification of 60 proteins involved in a wide range of activities and metabolisms. Very different patterns of protein expression were obtained according to conditions tested, highlighting the complexity of gravitropic responses. Our results suggest that primary and secondary tissues present specific mechanisms to sense reorientation and to respond to inclination. Some selected proteins are discussed.

Transcriptome profiling of peanut (Arachis hypogaea) gynophores in gravitropic response

“…Among the metabolism pathways identified, carbohydrate metabolism and amino acid metabolism are the two major pathways, following with energy metabolism, biosynthesis of other secondary metabolites, metabolism of terpenoids and polyketides, glycan biosynthesis and metabolism, and nucleotide metabolism. Similar to our results, transcriptome analysis in Arabidopsis exposed to gravity stimulation also revealed that metabolism is one of major gene groups responding to gravitropism (Kimbrough et al 2004;Kittang et al 2004) Among the metabolism pathways identified in this study, energy metabolism was also found to function in plants under gravitropic stimulation according to proteomic analysis (Azri et al 2009;Herrera et al 2010). In Arabidopsis, secondary metabolism genes were altered by magnetically induced hyperand microgravity at both transcription and translation levels (Manzano et al 2012;Herranz et al 2013).…”

“…In Arabidopsis, secondary metabolism genes were altered by magnetically induced hyperand microgravity at both transcription and translation levels (Manzano et al 2012;Herranz et al 2013). Proteome analysis of poplar stems exposed to gravitropic stimulation has led to determination of several pathways also identified in our study, including nucleotide metabolism, carbohydrate metabolism, photosynthesis and primary metabolism (energy) (Azri et al 2009). Millar and Kiss (2013) also showed the metabolic profile of Arabidopsis thalianna during gravitropism and phototropism, and identified carbohydrate metabolism, secondary metabolism and amino acid biosynthesis as the three main responding pathways.…”

(Not) Keeping the stem straight: a proteomic analysis of maritime pine seedlings undergoing phototropism and gravitropism

“…ATP synthase was detected as differentially expressed which could be explained by the high requirement of energy needed to quickly reorient in space. In an inclined poplar hybrid ( Populus tremula × Populus alba ) this protein was also identified suggesting that its over expression can be related to an energy production or in response to oxidative stress [36]. The accumulation of G3PDH and PGK involved in glucose degradation and the production of energy also suggest an active metabolism in the production of pyruvate, ATP and other intermediates.…”

Gravity sensing, a largely misunderstood trigger of plant orientated growth

“…In several gravitropism studies, the plant or the organ have been tilted without being staked before (Azri et al, 2009; Tocquard et al, 2014b). Although such conditions allowed gravitropic movements, they also allowed organ bending under its own weight.…”