Genomics and domestication of wheat: Modern wheat, which underlies the diet of many across the globe, has a long history of selection and crosses among different species. Avni et al. used the Hi-C method of genome confirmation capture to assemble and annotate the wild allotetraploid wheat ( Triticum turgidum ). They then identified the putative causal mutations in genes controlling shattering (a key domestication trait among cereal crops). They also performed an exome capture–based analysis of domestication among wild and domesticated genotypes of emmer wheat. The findings present a compelling overview of the emmer wheat genome and its usefulness in an agricultural context for understanding traits in modern bread wheat. Science , this issue p. 93

Summary: Drought is the major environmental factor limiting crop productivity worldwide. We hypothesized that it is possible to enhance drought tolerance by delaying stress‐induced senescence through the stress‐induced synthesis of cytokinins in crop‐plants. We generated transgenic rice (Oryza sativa) plants expressing an isopentenyltransferase (IPT) gene driven by P_SARK, a stress‐ and maturation‐induced promoter. Plants were tested for drought tolerance at two yield‐sensitive developmental stages: pre‐ and post‐anthesis. Under both treatments, the transgenic rice plants exhibited delayed response to stress with significantly higher grain yield (GY) when compared to wild‐type plants. Gene expression analysis revealed a significant shift in expression of hormone‐associated genes in the transgenic plants. During water‐stress (WS), P_SARK::IPT plants displayed increased expression of brassinosteroid‐related genes and repression of jasmonate‐related genes. Changes in hormone homeostasis were associated with resource(s) mobilization during stress. The transgenic plants displayed differential expression of genes encoding enzymes associated with hormone synthesis and hormone‐regulated pathways. These changes and associated hormonal crosstalk resulted in the modification of source/sink relationships and a stronger sink capacity of the P_SARK::IPT plants during WS. As a result, the transgenic plants had higher GY with improved quality (nutrients and starch content).

Intracellular Na⁺/H⁺ antiporters (NHXs) play important roles in cellular pH and Na⁺ and K⁺ homeostasis in all eukaryotes. Based on sequence similarity, the six intracellular Arabidopsis thaliana members are divided into two groups. Unlike the vacuolar NHX1-4, NHX5 and NHX6 are believed to be endosomal; however, little data exist to support either their function or localization. Using reverse genetics, we show that whereas single knockouts nhx5 or nhx6 did not differ from the wild type, the double knockout nhx5 nhx6 showed reduced growth, with smaller and fewer cells and increased sensitivity to salinity. Reduced growth of nhx5 nhx6 was due to slowed cell expansion. Transcriptome analysis indicated that nhx5, nhx6, and the wild type had similar gene expression profiles, whereas transcripts related to vesicular trafficking and abiotic stress were enriched in nhx5 nhx6. We show that unlike other intracellular NHX proteins, NHX5 and NHX6 are associated with punctate, motile cytosolic vesicles, sensitive to Brefeldin A, that colocalize to known Golgi and trans-Golgi network markers. We provide data to show that vacuolar trafficking is affected in nhx5 nhx6. Possible involvements of NHX5 and NHX6 in maintaining organelle pH and ion homeostasis with implications in endosomal sorting and cellular stress responses are discussed.

The effects of water deficit on carbon and nitrogen metabolism were investigated in flag leaves of wild-type and transgenic rice (Oryza sativajaponica ‘Kitaake’) plants expressing ISOPENTENYLTRANSFERASE (IPT; encoding the enzyme that mediates the rate-limiting step in cytokinin synthesis) under the control of P_SARK, a maturation- and stress-induced promoter. While the wild-type plants displayed inhibition of photosynthesis and nitrogen assimilation during water stress, neither carbon nor nitrogen assimilation was affected by stress in the transgenic P_SARK::IPT plants. In the transgenic plants, photosynthesis was maintained at control levels during stress and the flag leaf showed increased sucrose (Suc) phosphate synthase activity and reduced Suc synthase and invertase activities, leading to increased Suc contents. The sustained carbon assimilation in the transgenic P_SARK::IPT plants was well correlated with enhanced nitrate content, higher nitrate reductase activity, and sustained ammonium contents, indicating that the stress-induced cytokinin synthesis in the transgenic plants played a role in maintaining nitrate acquisition. Protein contents decreased and free amino acids increased in wild-type plants during stress, while protein content was preserved in the transgenic plants. Our results indicate that the stress-induced cytokinin synthesis in the transgenic plants promoted sink strengthening through a cytokinin-dependent coordinated regulation of carbon and nitrogen metabolism that facilitates an enhanced tolerance of the transgenic plants to water deficit.