Translation of specific plant mRNAs is differentially regulated under certain abiotic stress conditions such as heat, oxygen deprivation and dehydration. The majority of transcripts exhibit varying degrees of translational repression, whereas a subset of transcripts escape such repression and remain actively translated. The underlying mechanisms that mediate this control, and in particular the identities of the regulatory RNA elements involved, remain poorly understood. Using a combined computational and experimental approach, we identified a novel cis-regulatory element in the 5 0 -untranslated region (5 0 -UTR) that affects differential translation in response to heat stress (HS) in Arabidopsis thaliana. First, we selected a set of genes with distinct translational responses to HS, based on our previously reported genome-wide data regarding changes in polysome loading induced by HS in A. thaliana cultured cells. We evaluated the 5 0 -UTRs of these messages for their ability to mediate expression, when fused to reporter mRNAs, in protoplasts under HS. The data from the reporter assay and the nucleotide sequences of the 5 0 -UTRs tested were used to define regulatory elements in the 5 0 -UTRs, with the help of a partial least square (PLS) regression model. The computational analysis using PLS and subsequent experimental characterization of a series of 5 0 -UTR mutants provided evidence that the 5 0 -proximal sequence of the 5 0 -UTR is a primary and position-dependent determinant of 5 0 -UTR-mediated differential translation in response to HS. Finally, we discuss the possible mechanism underlying HS regulation of differential mRNA translation.

For higher expression of a foreign gene in plant cells, it is important to optimize nucleotide sequences corresponding to 5′-untranslated region (5′-UTR), because it usually has great impacts on the expression of the gene mainly at the translational level. In this study, with an aim to nd useful 5′-UTRs, thirty nine 5′-UTRs derived from Arabidopsis thaliana genes were tested by transient expression of re y luciferase (Fluc), and that of A. thaliana arabinogalactanprotein 21 (AtAGP21) gene was selected for further analyses. Its activity was either equaling or surpassing that of known translational enhancer, A. thaliana alchol dehydrogenase (AtADH) 5′-UTR in dicotyledons, and was further improved by the optimizing sequence context of the initiating codon (−3 to −1 of AUG). Finally, we also found that the modi ed AtAGP21 5′-UTR was useful in recombinant expression of horseradish peroxidase (HRP) in tobacco cultured cells, and the yield was as much as 23 mg l −1 culture medium in seven days.

Sloped sidewalls in 4H-SiC mesa structures on the (000-1) C face were formed by a Cl2-O2 thermal etching method. The etching rate of 4H-SiC (000-1) C face was 10 times faster than that of (0001) Si face, and the etching rate at 910oC was about 18μm/h. The etched surface was rather smooth, and the sidewall of the mesa was inclined to the off-axis substrate. Taking into account the off angle of about 8o toward [11-20] off direction, the angles of the sidewalls were 52-56o for the <1-100> and 55-57o for the <11-20> directions from the crystallographically accurate (000-1) C face. Epitaxial pn junction diodes with the sloped sidewalls structure were fabricated, which had good electrical properties.

By the use of Cl2-O2 thermal etching method, the etching rates of 4H-SiC were reached to about 1μm/h for Si and 40μm/h for C face at 950oC. Etch pits only appeared over 0.25-μm-etched depth on the 4H-SiC (0001) Si face. The shapes and density of etch pits are similar tendencies in the case of molten KOH etched surface. To study the relationship between thermally etched surface features and crystal defects, the planar mapping electron-beam-induced current (EBIC) technique was carried out. Almost dark areas in the EBIC image correspond to the etch pits. From the EBIC image, a shell-like pit formed by the Cl2-O2 etching on the (0001) Si face is a basal plane dislocation.