The deployment of heterosis in the form of hybrid rice varieties has boosted grain yield, but grain quality improvement still remains a challenge. Here we show that a quantitative trait locus for rice grain quality, qGW7, reflects allelic variation of GW7, a gene encoding a TONNEAU1-recruiting motif protein with similarity to C-terminal motifs of the human centrosomal protein CAP350. Upregulation of GW7 expression was correlated with the production of more slender grains, as a result of increased cell division in the longitudinal direction and decreased cell division in the transverse direction. OsSPL16 (GW8), an SBP-domain transcription factor that regulates grain width, bound directly to the GW7 promoter and repressed its expression. The presence of a semidominant GW7(TFA) allele from tropical japonica rice was associated with higher grain quality without the yield penalty imposed by the Basmati gw8 allele. Manipulation of the OsSPL16-GW7 module thus represents a new strategy to simultaneously improve rice yield and grain quality.

Coordination of shoot photosynthetic carbon fixation with root inorganic nitrogen uptake optimizes plant performance in a fluctuating environment [1]. However, the molecular basis of this long-distance shoot-root coordination is little understood. Here we show that Arabidopsis ELONGATED HYPOCOTYL5 (HY5), a bZIP transcription factor that regulates growth in response to light [2, 3], is a shoot-to-root mobile signal that mediates light promotion of root growth and nitrate uptake. Shoot-derived HY5 auto-activates root HY5 and also promotes root nitrate uptake by activating NRT2.1, a gene encoding a high-affinity nitrate transporter [4]. In the shoot, HY5 promotes carbon assimilation and translocation, whereas in the root, HY5 activation of NRT2.1 expression and nitrate uptake is potentiated by increased carbon photoassimilate (sucrose) levels. We further show that HY5 function is fluence-rate modulated and enables homeostatic maintenance of carbon-nitrogen balance in different light environments. Thus, mobile HY5 coordinates light-responsive carbon and nitrogen metabolism, and hence shoot and root growth, in a whole-organismal response to ambient light fluctuations.

Background: High-cost production of bioplastics polyhydroxyalkanoates (PHA) is a major concern for their large scale application. In order to produce PHA economically, new technology must be developed to reduce costs on energy consumption, fresh water and substrate usages. It is also important to conduct the PHA production process in a continuous way rather than in a batch process. Results: A halophile Halomonas campaniensis strain LS21 was isolated to allow the development of a sea water based open and continuous process for PHA production utilizing mixed substrates consisting of mostly cellulose, starch, lipids and proteins. To study the feasibilities of open and long-term cultivation as well as genetic manipulation of this strain, polyhydroxybutyrate (PHB), the first member of the diverse PHA family, was taken as an example for the application of H. campaniensis LS21 in a robust and long lasting fermentation process. Wild type and recombinant H. campaniensis LS21 containing a PHB synthesis genes phbCAB were allowed respectively to grow in artificial seawater containing mixed substrates similar to kitchen wastes, including soluble and insoluble cellulose, proteins, fats, fatty acids and starch for 65 days without interruption. In the presence of 27 g/L NaCl under a pH around 10 at 37°C, the recombinant produced approximately 70% PHB and the wild type 26% during the 65 days fermentation process without infection. H. campaniensis LS21 secreted extracellular amylase, lipase, protease and cellulase simultaneously during the whole process to allow consumption of the mixed substrates. The recombinant was also found to stably maintain the phbCAB plasmid over the entire 65 days process. Conclusions:The seawater based open and continuous process based on halophilic Halomonas campaniensis LS21 allowed the applications of kitchen wastes like mixed substrates as nutrients for production of bioplastic PHB. This study demonstrates the advantages of this technology in terms of energy saving (non-sterilization), seawater based (not fresh water needed), long-lasting and continuous open processing (against batch process), and low cost substrates (non-food mixed substrates). Combined with its ease of genetic manipulation, Halomonas campaniensis LS21 could be developed into a platform for low cost production of chemicals, materials and biofuels.