Resistance of transgenic rice events (rbcS:cry1Ac) against three lepidopteran rice pests

The transgenic rice expressing cry1Ac gene, which is linked to the rice rbcS promoter and its transit peptide sequence (tp), was highly resistant against all instars of Cnaphalocrocis medinalis (Guenetée) (Lepidoptera: Crambidae). In this study, we evaluated the larval mortality, behavior change, and field occurrence of three main rice pests, C. medinalis, Naranga aenescens (Moore) (Lepidoptera: Noctuidae), and Parnara guttata (Bremer & Grey) (Lepidoptera: Hesperiidae) in T4 generations of three Bt rice events (rbcS3:cry1Ac; 608102, 608104 and 608107) and non-Bt rice. All of the three Bt rice events were resistant to C. medinalis which showed significantly higher mortality for all instars compared to non-Bt rice. The resistance of Bt rice events against the larvae decreased gradually as the larvae developed. However, the survived larvae which ingested Bt rice events died eventually without further development. The resistance of three Bt rice events was investigated in the pot test, which was conducted with 3rd instars of C. medinalis, N. aenescens, and P. guttata, showed mortalities of over 70%. In behavioral assay, C. medinalis fed on the Bt rice events showed feeding avoidance and less leaf rolling behavior compared to that of the larvae fed on non-Bt rice. A 2-yr field survey conducted with larvae of C. medinalis and P. guttata also showed that the three Bt rice events significantly had lower damaged on leaves compared to that of non-Bt rice. Overall, the three Bt rice events were highly resistant to the larvae of lepidopteran target rice pests.     

AlLTPs from Allium species represent a novel class of lipid transfer proteins that are localized in endomembrane compartments

Lipid transfer proteins (LTPs) are widely distributed in the plant kingdom, but their functions remain elusive. The proteins AlLTP2-4 were isolated from three related Allium plants: garlic (A. sativum L.), Welsh onion (A. fistulosum L.), and Nanking shallot (A. ascalonicum L.). These novel proteins comprise a new class of LTPs associated with the Ace-AMP1 from onion (A. cepa L.). The AlLTP genes encode proteins harboring 132 common amino acids and also share a high level of sequence identity. Protein characteristics and phylogenetic analysis suggest that LTPs could be classified into five distinct groups. The AlLTPs were clustered into the most distantly related plant LTP subfamily and appeared to be restricted to the Allium species. In particular, the number of amino acids existing between the fourth and fifth Cys residue was suggested as a conserved motif facilitating the categorization of all the LTP-related proteins in the family. Unlike other LTPs, AlLTPs harboring both the putative C-terminal propeptide and N-terminal signal peptide were predicted to be localized to cytoplasmic vacuoles. When a chimeric GFP protein fused with both N-terminal and C-terminal AlLTP2 signal peptides was expressed in rice cells, the fluorescence signal was detected in the endomembrane compartments, thereby confirming that AlLTPs are an unprecedented intracellular type of LTP. Collectively, our present data demonstrate that AlLTPs are a novel type of LTP associated with the Allium species.     

Arabidopsis CBF3/DREB1A and ABF3 in transgenic rice increased tolerance to abiotic stress without stunting growth

Rice (Oryza sativa), a monocotyledonous plant that does not cold acclimate, has evolved differently from Arabidopsis (Arabidopsis thaliana), which cold acclimates. To understand the stress response of rice in comparison with that of Arabidopsis, we developed transgenic rice plants that constitutively expressed CBF3/DREB1A (CBF3) and ABF3, Arabidopsis genes that function in abscisic acid-independent and abscisic acid-dependent stress-response pathways, respectively. CBF3 in transgenic rice elevated tolerance to drought and high salinity, and produced relatively low levels of tolerance to low-temperature exposure. These data were in direct contrast to CBF3 in Arabidopsis, which is known to function primarily to enhance freezing tolerance. ABF3 in transgenic rice increased tolerance to drought stress alone. By using the 60 K Rice Whole Genome Microarray and RNA gel-blot analyses, we identified 12 and 7 target genes that were activated in transgenic rice plants by CBF3 and ABF3, respectively, which appear to render the corresponding plants acclimated for stress conditions. The target genes together with 13 and 27 additional genes are induced further upon exposure to drought stress, consequently making the transgenic plants more tolerant to stress conditions. Interestingly, our transgenic plants exhibited neither growth inhibition nor visible phenotypic alterations despite constitutive expression of the CBF3 or ABF3, unlike the results previously obtained from Arabidopsis where transgenic plants were stunted.     

Characterization of the root-predominant gene promoter HPX1 in transgenic rice plants

Gene promoter(s) specialized in root tissues is an important component for crop biotechnology. In our current study, we report results of promoter analysis of the HPX1, a gene expressed predominantly in roots. The HPX1 promoter regions were predicted, linked to the gfp reporter gene, and transformed into rice. Promoter activities were analyzed in various organs and tissues of six independent transgenic HPX1:gfp plants using the fluorescent microscopy and q-RT-PCR methods. GFP fluorescence levels were high in root elongation regions but not in root apex and cap of the HPX1:gfp plants. Very low levels of GFP fluorescence were observed in anthers and leaves. Levels of promoter activities were 16- to 190-fold higher in roots than in leaves of the HPX1:gfp plants. The HPX1 promoter directs high levels of gene expression in root tissues producing GFP levels up to 0.39 % of the total soluble protein. Thus, the HPX1 promoter is predominantly active in the root elongation region during the vegetative stage of growth.