The wild progenitor (Oryza rufipogon) of Asian rice (Oryza sativa) shows a wide range of variations in lifehistory traits, forming an annual-perennial continuum. A conspicuous feature of an annual type of wild rice is represented by its adaptability to disturbed habitats, and its short stature with many tillers and a prostrate growth habit. The present study was carried out to examine the genetic differentiation between wild annual and cultivated (Japonica type) rice strains by quantitative trait locus (QTL) analysis. In total, 20 adaptive and/ or domestication-related traits were evaluated in recombinant inbred lines (RILs). A total of 28 putative QTLs were detected across the genome. Six QTLs responsible for plant architecture were located on the short arm of chromosome 7. The near-isogenic line with the region containing the QTL cluster confirmed that the QTLs exerted a significant effect on the plant architecture in the genetic background of cultivated rice. A similar QTL cluster was also found in another annual strain of a different origin, suggesting that the QTL cluster might be predominant in annual wild rice. Furthermore, a QTL for tolerance to disturbance (simulated trampling) was detected within the region of the cluster on chromosome 7. These results are discussed in relation to their ecological significance in wild annuals of rice.

EnvZ is a histidine protein kinase important for osmoregulation in bacteria. While structural data are available for this enzyme, the nucleotide binding pocket is not well characterized. The ATP binding domain (EnvZB) was expressed, and its ability to bind nucleotide derivatives was assessed using equilbrium and stopped-flow fluorescence spectroscopy. The fluorescence emission of the trinitrophenyl derivatives, TNP-ATP and TNP-ADP, increase upon binding to EnvZB. The fluorescence enhancements were quantitatively abolished in the presence of excess ADP, indicating that the fluorescent probes occupy the nucleotide binding pocket. Both TNP-ATP and TNP-ADP bind to EnvZB with high affinity (K(d) = 2-3 microM). The TNP moiety attached to the ribose ring does not impede access of the fluorescent nucleotide into the binding pocket. The association rate constant for TNP-ADP is 7 microM(-1) s(-1), a value consistent with those for natural nucleotides and the eucaryotic protein kinases. Using competition experiments, it was found that ATP and ADP bind 30- and 150-fold more poorly, respectively, than the corresponding TNP-derivatized forms. Surprisingly, the physiological metal Mg(2+) is not required for ADP binding and only enhances ATP affinity by 3-fold. Although portions of the nucleotide pocket are disordered, the recombinant enzyme is highly stable, unfolding only at temperatures in excess of 70 degrees C. The unusually high affinity of the TNP derivatives compared to the natural nucleotides suggests that hydrophobic substitutions on the ribose ring enforce an altered binding mode that may be exploited for drug design strategies.

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