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...

Purpose of Review Prostate cancer is one of the most common cancers in men and accounts for about 10% of all new cancer cases in the USA. Despite significant improvements in survival, it is estimated that deaths from prostate cancer in 2019 will exceed 30,000 individuals. Here, we review plant-derived bioactive compounds with the ability to modulate the growth of prostate cancer cells. These compounds represent potential therapeutic alternatives for the prevention and treatment of prostate cancer. Recent Findings Numerous plants produce phytochemicals that are important for their development and protection. Many of these compounds have inhibitory effects on the growth of cancer cells. Summary Cancers are a leading cause of death worldwide and treatments tend to be costly with many negative side effects. Identification of new potential chemo-therapeutic and chemo-protective compounds that have little or no negative effects on normal cells is therefore of great importance.

The scaffold protein receptor for Activated C Kinase1 (RACK1) regulates multiple aspects of plants, including seed germination, growth, environmental stress responses, and flowering. Recent studies have revealed that RACK1 is associated with NADPH-dependent reactive oxygen species (ROS) signaling in plants. ROS, as a double-edged sword, can modulate several developmental pathways in plants. Thus, the resulting physiological consequences of perturbing the RACK1 expression-induced ROS balance remain to be explored. Herein, we combined molecular, pharmacological, and ultrastructure analysis approaches to investigate the hypothesized connection using T-DNA-mediated activation-tagged RACK1B overexpressed (OX) transgenic rice plants. In this study, we find that OsRACK1B-OX plants display reduced pollen viability, defective anther dehiscence, and abnormal spikelet morphology, leading to partial spikelet sterility. Microscopic observation of the mature pollen grains from the OX plants revealed abnormalities in the exine and intine structures and decreased starch granules in the pollen, resulting in a reduced number of grains per locule from the OX rice plants as compared to that of the wild-type (WT). Histochemical staining revealed a global increase in hydrogen peroxide (H2O2) in the leaves and roots of the transgenic lines overexpressing OsRACK1B compared to that of the WT. However, the elevated H2O2 in tissues from the OX plants can be reversed by pre-treatment with diphenylidonium (DPI), an NADPH oxidase inhibitor, indicating that the source of H2O2 could be, in part, NADPH oxidase. Expression analysis showed a differential expression of the NADPH/respiratory burst oxidase homolog D (RbohD) and antioxidant enzyme-related genes, suggesting a homeostatic mechanism of H2O2 production and antioxidant enzyme activity. BiFC analysis demonstrated that OsRACK1B interacts with the N-terminal region of RbohD in vivo. Taken together, these data indicate that elevated OsRACK1B accumulates a threshold level of ROS, in this case H2O2, which negatively regulates pollen development and fertility. In conclusion, we hypothesized that an optimal expression of RACK1 is critical for fertility in rice plants.

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