Arabidopsis lenc1 mutant displays reduced ABA accumulation by low AtNCED3 expression under osmotic stress.

The plant hormone, abscisic acid (ABA), is a main signal transducer that confers abiotic stress tolerance to plants. Although the pathway of ABA production and the genes catalyzing its biosynthesis are largely defined, the regulatory mechanism of ABA biosynthesis in response to abiotic stress remains much unknown. In this study, to identify upstream genes regulating ABA biosynthesis involved in abiotic stress signal transduction, Arabidopsis thaliana mutants with altered promoter activity of 9-cis-epoxycarotenoid dioxygenase 3 (NCED3), a key gene in ABA biosynthesis, were identified and characterized. Among selected mutants, lenc1 (for low expression of NCED3 1) after dehydration treatment had lower AtNCED3 promoter activity compared with wild type. lenc1 mutation is recessive and is located on chromosome 4. Expression analysis of AtNCED3 and quantification of ABA levels showed that both the AtNCED3 transcripts and the endogenous ABA in lenc1 were less abundant than in wild type under dehydration treatments. The lenc1 was hypersensitive to methyl viologen (MV), LiCl, NaCl and high light. The aerial part of lenc1 lost water faster than wild type possibly due to a larger stomata opening. Our results suggest LENC1 might act as a positive regulator in AtNCED3 gene expression under osmotic stress.

Loss of peripheral polypeptides in the stromal side of photosystem I by light-chilling in cucumber leaves.

Photosystem I (PSI) is severely damaged by chilling at 4 degrees C in low light, especially in the chilling sensitive plant cucumber. To investigate the early events in PSI photoinhibition, we examined structural changes in the level of pigment-protein complexes in cucumber leaves in comparison with pea leaves. The complexes were separated on a native green gel and an increase in the intensity of a band was observed only in light-chilled cucumber leaves. The 77 K fluorescence emission spectrum of this green band indicated that the band was mainly composed of PSI with light-harvesting complex I. Each lane was cut from the green gel and separated on a fully denaturing SDS-PAGE in the second dimension. The new green gel band observed after light-chilling in cucumber leaves lacked 19, 18, and 16.5 kDa polypeptides. These results suggest that light-chilling facilitates the release of three peripheral polypeptides as an early event of chilling stress in vivo, which results in the inactivation of PSI in intact cucumber leaves.

Generation and analysis of end sequence database for T-DNA tagging lines in rice.

We analyzed 6749 lines tagged by the gene trap vector pGA2707. This resulted in the isolation of 3793 genomic sequences flanking the T-DNA. Among the insertions, 1846 T-DNAs were integrated into genic regions, and 1864 were located in intergenic regions. Frequencies were also higher at the beginning and end of the coding regions and upstream near the ATG start codon. The overall GC content at the insertion sites was close to that measured from the entire rice (Oryza sativa) genome. Functional classification of these 1846 tagged genes showed a distribution similar to that observed for all the genes in the rice chromosomes. This indicates that T-DNA insertion is not biased toward a particular class of genes. There were 764, 327, and 346 T-DNA insertions in chromosomes 1, 4 and 10, respectively. Insertions were not evenly distributed; frequencies were higher at the ends of the chromosomes and lower near the centromere. At certain sites, the frequency was higher than in the surrounding regions. This sequence database will be valuable in identifying knockout mutants for elucidating gene function in rice. This resource is available to the scientific community at http://www.postech.ac.kr/life/pfg/risd.