Improving crop phosphorus (P) uptake and use capabilities is needed to alleviatehunger and increase sustainability. The rice ( Oryza sativa L.) protein kinase P HOSPHORUS- S TARVATION TOL ERANCE 1 ( OsPSTOL1 ), which is absent from many modern varieties, increases root growth and stimulates yield under P deficient conditions. A biogeographic survey of genetic variation in OsPSTOL1 demonstrates its loss in a subset of japonica rice after the temperate-tropical split and typical absence in paddy varieties of east Asia. Additional loss-of-function alleles have accumulated in countries with high fertilizer use and irrigation control, suggesting that OsPSTOL1 may be less favorable or unnecessary in those conditions. OsPSTOL1 homologues are present in agronomic crop species. OsPSTOL1 is an unusual family member due to its presence of a kinase domain and loss of a transmembrane domain; a similarly truncated OsPSTOL1 -like gene is present in bread wheat ( Triticum aestivum L.). Overexpression of OsPSTOL1 in wheat confers an increase in shoot and root growth under low P conditions, as well as a more rapid induction of the core low P response pathway. This work suggests that OsPSTOL1 acts on an evolutionarily conserved mechanism in wheat that may be utilized for crop improvement.

Oxygen deficient plants suffer an energy limitation that can suppress growth and development and lead to premature cell death. Underlying adaptation, plants have evolved integrated genetic and cellular programs to respond to low oxygen stress (hypoxia/anoxia). Mechanisms of diverse adaptation share common themes, such as enhanced oxygen-independent energy supply, regulated growth and energy consumption, and prioritization of energy use. Tailored protein synthesis conserves energy by reduction in synthesis of non-stress-relevant proteins (90% of cellular mRNA) involved in normal growth and development, and funnels resources to translation of hypoxia-induced mRNAs encoding proteins that drive carbohydrate mobility and substrate-level phosphorylation. It was hypothesized that the mRNAs that are translationally repressed during hypoxia associate with RNA binding proteins, which protect them or allow their degradation, and facilitate their rapid return of the sequestered mRNAs to translational complexes within minutes of reoxygenation. Stress granules (SGs) and processing bodies (PBs) are two structures of up to 4 µM in diameter, characterized in non-plant eukaryotic cells as sites of mRNA sequestration and degradation during stress. Conservation of genes encoding orthologs of these proteins in plants suggests a corresponding system for management of cytosolic non-translated mRNA . We initiated a survey study of predicted RNA binding proteins that are orthologous to non-plant SG and PB proteins encoded by Arabidopsis thaliana. To determine their roles in normal development, T-DNA insertion mutant alleles were identified and surveyed for abnormal growth and development. In addition, several were fused to fluorescent proteins to determine their subcellular localization and make observations of the effect of overexpression on normal growth. From this survey, plant OLIGOURIDYLATE BINDING PROTEIN (UBP)1C was further characterized for its role during hypoxia stress. UBP1A and UBP1C-GPF fusion proteins relocalized from diffuse to granular cytoplasmic localization upon hypoxia treatment, which was rapidly reversed by reoxygenation, concomitant with restoration of protein synthesis. These granules required completion of translation for their assembly. Mutation of these genes led to altered survival of oxygen deprivation. Global quantitative profiling of the mRNAs associated with UBP1C revealed that transcripts with U-rich 3'-untranslated regions are highly UBP1C-associated during non-stress conditions. Upon treatment with hypoxia most cellular mRNAs increased association with UBP1C with the exception of the mRNAs that were highly induced by hypoxia and associated with polyribosomes under stress and those already highly associated. Upon reoxygenation this association was rapidly reversed. In conclusion, UBP1C association with mRNA during hypoxia is linked to the dynamic sequestration and turnover of transcripts observed during hypoxia in the model plant Arabidopsis thaliana.

A formidable challenge in the genomic era is the assignment of structure and function to unknown genes in model organisms. Forward chemical genetics seeks to discover and characterize pathways through the identification of novel phenotypes induced by organic small molecules and subsequent isolation of their target gene(s). Downstream

genetic and biochemical strategies to dissect the action of bioactive molecules are often hampered by weak target-ligand interactions, low target abundance, genetic factors, and synthetic inaccessibility of analogs. We present a synthetic scaffold that simultaneously permits fluorescence detection and photoaffinity labeling (diazirine) in a combinatorial library of thousands of drug-like small molecules synthesized through click chemistry. Using this library, we identified several bioactives that alter seedling growth of the model plant Arabidopsis thaliana and generated candidate ethyl methanesulfonate-induced resistant mutants for downstream simple sequence length polymorphism marker-assisted mapping and single nucleotide polymorphism identification by Illumina next-generation DNA sequencing. Our proof-of-principle study will facilitate target identification of novel bioactives and accelerate chemical genetics discoveries.