Arabidopsis scaffold protein RACK1A modulates rare sugar D-allose regulated gibberellin signaling

Abstract

Rare sugars-monosaccharides that rarely exist in nature-are known to regulate diverse physiological responses in both plants and animals. With the advent of the discovery of "Izumoring," an in vitro enzymatic approach to the synthesis of all rare sugars, 1,2 research in this area has implicated rare sugars in many physiological conditions. These include but are not limited to the immunosuppressive activity in liver transplantation, 3 protection against liver ischemia reperfusion injury, 4,5 protection from reactive oxygen species (ROS) 6,7 and anticancer activity on different cancer cell lines. [8][9][10][11] Although not abundant, rare sugars-Dallose, D-psicose, D-allitol, L-galactose, tagatose or their derivatives-have been found in the tissues of higher plants as well. [12][13][14][15][16][17][18] It was found that D-psicose inhibits plant root growth via hexokinase-independent pathway; it also inhibits bacterial blight disease in rice.19,20 D-allose was found to inhibit the rice growth and prevent bacterial blight disease in rice as well. 21 Recently, Akimitsu's group, a pioneer in rare sugar research, through the use of powerful genetics study has shown that the rare sugar D-allose suppresses GA signaling pathway in rice. 22D-allose strongly inhibited GA mediated α-amylase induction in embryo-less rice half seeds, 22 implicating a negative role of D-allose in the GA pathway. Earlier, we have shown that as energy sources and structural components, sugars are the central regulators of plant growth and development. in addition to the abundant natural sugars in plants, more than 50 different kinds of rare sugars exist in nature, several of which show distinct roles in plant growth and development. recently, one of the rare sugars, D-allose, an epimer of D-glucose at C3, is found to suppress plant hormone gibberellin (Ga) signaling in rice. Scaffold protein raCK1a in the model plant arabidopsis is implicated in the Ga pathway as rack1a knockout mutants show insensitivity to Ga in Ga-induced seed germination. using genetic knockout lines and a reporter gene, the functional role of raCK1a in the D-allose pathway was investigated. it was found that the rack1a knockout seeds showed hypersensitivity to D-alloseinduced inhibition of seed germination, implicating a role for raCK1a in the D-allose mediated suppression of seed germination. on the other hand, a functional raCK1a in the background of the double knockout mutations in the other two raCK1 isoforms, rack1b/rack1c, showed significant resistance to the D-allose induced inhibition of seed germination. the collective results implicate the raCK1a in the D-allose mediated seed germination inhibition pathway. Elucidation of the rare sugar signaling mechanism will help to advance understanding of this less studied but important cellular signaling pathway. Abbreviations: GA, gibberellin; RACK1, receptor for activated C kinase 1; MS, murashige and skoog Arabidopsis scaffold protein RACK1A (Receptor for Activating C Kinase 1) positively regulates GA signaling pathway a...

A role for seed storage proteins inArabidopsisseed longevity

“…RACK1 is a multi-function protein that plays a regulatory role in diverse signal transduction pathways and its transcripts are present during seed germination ( Chen et al , 2006 ; Guo et al , 2009 ). In Arabidopsis , the translation initiation factor eIF6-2 interacts with RACK1, a negative regulator of ABA response and positive regulator of GA signalling ( Guo et al , 2011 ; Fennell et al , 2012 ). It was demonstrated that ABA inhibited RACK1 and eIF6 gene expression ( Guo et al , 2011 ).…”

The Receptor for Activated C Kinase in Plant Signaling: Tale of a Promiscuous Little Molecule

“…thaliana RACK1 isogenes AtRACK1A, B , and C , although a functional redundancy derived from the high sequence conservation was expected and subsequently confirmed (Guo and Chen, 2008 ). The involvement of RACK1 in multiple plant hormonal pathways was confirmed by the study of hormonal treatments and developmental processes of loss-of-function Arabidopsis rack1a mutants (Chen et al, 2006 ; Fennell et al, 2012 ). The rack1a mutants displayed defects in seed germination, flowering, and production of leaves.…”

“…Interestingly, it was found in a different work that the AtRACK1A isoform seems to specifically mediate gibberellin signaling, at least in a D-allose mediated inhibition pathway (Fennell et al, 2012 ). When gibberellin was applied to Arabidopsis seeds, a significant up-regulation of AtRACK1A:GFP expression in the embryo root tip region of seedlings was observed after 72 h. The opposite effect was observed by treatment with the rare sugar D-allose, which is an inhibitor of seed germination (Fennell et al, 2012 ). Further analysis on Arabidopsis rack1a knockout mutants showed a significantly higher hypersensitivity to D-allose inhibition of germination compared to wild type seeds, and this inhibition was not counteracted by the addition of gibberellin.…”

Arabidopsis Receptor of Activated C Kinase1 Phosphorylation by WITH NO LYSINE8 KINASE

“…Like its counterpart in mammals, plant RACK1 protein interacts with nearly 100 proteins that fall into many different functional categories (Guo et al, 2007;Klopffleisch et al, 2011;Olejnik et al, 2011;Kundu et al, 2013). RACK1 is involved in plant hormone signaling (McKhann et al, 1997;Perennes et al, 1999;Chen et al, 2006aChen et al, , 2006bGuo et al, 2009aGuo et al, , 2009bFennell et al, 2012), leaf and root development (Guo and Chen, 2008;Guo et al, 2009b), drought and salt stress responses (Ullah et al, 2008;Guo et al, 2009a), flooding stress (Komatsu et al, 2014), nodulation (Islas-Flores et al, 2011, seed germination (Komatsu et al, 2005;Islas-Flores et al, 2009;Zhang et al, 2014), hydrogen peroxide production (Zhang et al, 2014), innate immunity (Nakashima et al, 2008), plant response to fungal pathogens (Wang et al, 2014), association with ribosomes (Chang et al, 2005;Giavalisco et al, 2005), protein translation (Guo et al, 2011), and microRNA abundance (Speth et al, 2013). However, little is known about the molecular mechanism of action of RACK1.…”