Heterologous expression of the AtDREB1A gene in chrysanthemum increases drought and salt stress tolerance

DNA cassette containing an AtDREB1A cDNA and a nos terminator, driven by a cauliflower mosaic 35S promoter, or a stress-inducible rd29A promoter, was transformed into the ground cover chrysanthemum (Dendranthema grandiflorum) ‘Fall Color’ genome. Compared with wild type plants, severe growth retardation was observed in 35S:DREB1A plants, but not in rd29A:DREB1A plants. RT-PCR analysis revealed that, under stress conditions, the DREB1A gene was over-expressed constitutively in 35S:DREB1A plants, but was over-expressed inductively in rd29A:DREB1A plants. The transgenic plants exhibited tolerance to drought and salt stress, and the tolerance was significantly stronger in rd29A:DREB1A plants than in 35S:DREB1A plants. Proline content and SOD activity were increased inductively in rd29A:DREB1A plants than in 35S:DREB1A plants under stress conditions. These results indicate that heterologous AtDREB1A can confer drought and salt tolerance in transgenic chrysanthemum, and improvement of the stress tolerance may be related to enhancement of proline content and SOD activity.     

Antisense suppression of proline degradation improves tolerance to freezing and salinity in Arabidopsis thaliana

The location of tryptophan residues in the actin macromolecule was studied on the basis of the known 3D structure. For every tryptophan residue the polarity and packing density of their microenvironments were evaluated. To estimate the accessibility of the tryptophan residues to the solvent molecules it was proposed to analyze the radial dependence of the packing density of atoms in the macromolecule about the geometric center of the indole rings of the tryptophan residues. The proposed analysis revealed that the microenvironment of tryptophan residues Trp-340 and Trp-356 has a very high density. So these residues can be regarded as internal and inaccessible to solvent molecules. Their microenvironment is mainly formed by non-polar groups of protein. Though the packing density of the Trp-86 microenvironment is lower, this tryptophan residue is apparently also inaccessible to solvent molecules, as it is located in the inner region of macromolecule. Tryptophan residue Trp-79 is external and accessible to the solvent. All residues that can affect tryptophan fluorescence were revealed. It was found that in the close vicinity of tryptophan residues Trp-79 and Trp-86 there are a number of sulfur atoms of cysteine and methionine residues that are known to be effective quenchers of tryptophan fluorescence. The most essential is the location of SG atom of Cys-10 near the NE1 atom of the indole ring of tryptophan residue Trp-86. On the basis of microenvironment analysis of these tryptophan residues and the evaluation of energy transfer between them it was concluded that the contribution of tryptophan residues Trp-79 and Trp-86 must be low. Intrinsic fluorescence of actin must be mainly determined by two other tryptophan residues--Trp-340 and Trp-356. It is possible that the unstrained conformation of tryptophan residue Trp-340 and the existence of aromatic rings of tyrosine and phenylalanine and proline residues in the microenvironments of tryptophan residues Trp-340 and Trp-356 are also essential to their blue fluorescence spectrum.     

Functional analysis of the 37 kDa inner envelope membrane polypeptide in chloroplast biogenesis using a Ds-tagged Arabidopsis pale-green mutant

To study the functions of the nuclear genes involved in chloroplast development, we systematically analyzed albino and pale-green Arabidopsis thaliana mutants by using a two-component transposon system based on the Ac/Ds element of maize as a mutagen. One of the pale-green mutants, albino or pale green mutant 1 (designated as apg1), did not survive beyond the seedling stage, when germinated on soil. The chloroplasts of the apg1 plants contained decreased numbers of lamellae with reduced levels of chlorophyll. A gene encoding a 37 kDa polypeptide precursor of the chloroplast inner envelope membrane was disrupted by insertion of the Ds transposon in apg1. The 37 kDa protein had partial sequence similarity to the S-adenosylmethionine-dependent methyltransferase. The apg1 plants lacked plastoquinone (PQ), suggesting that the APG1 protein is involved in the methylation step of PQ biosynthesis, which is localized at the envelope membrane. Our results demonstrate the importance of the 37 kDa protein of the chloroplast inner envelope membrane for chloroplast development in Arabidopsis.     

Identification of a gene family (kat) encoding kinesin-like proteins in Arabidopsis thaliana and the characterization of secondary structure of KatA

A gene family, designated kat, has been characterized in Arabidopsis thaliana by genomic Southern hybridization and nucleotide sequencing analysis. The kat gene family includes at least five members, named katA, katB, katC, katD and katE, whose products share appreciable sequence similarities in their presumptive ATP-binding and microtubule-binding motifs with known kinesin-like proteins. The carboxyl-terminal region of the KatA protein deduced from the nucleotide sequence of the cDNA clone has considerable homology with the mechanochemical motor domain of the kinesin heavy chain. The predicted secondary structure of the KatA protein indicates two globular domains separated by a long a helical coiled coil with heptad repeat structures, such as are commonly found in kinesin-like proteins.     

Cloning of cDNAs for genes that are early-responsive to dehydration stress (ERDs) inArabidopsis thaliana L.: identification of three ERDs as HSP cognate genes

InArabidopsis thaliana L., accumulation of abscisic acid (ABA) began to increase 2 h after plants had been subjected to dehydration stress and reached maximum levels after 10h. Differential hybridization was used to isolate 26Arabidopsis cDNAs with gene expression induced by a 1 h dehydration treatment. The cDNA clones were classified into 16 groups based on Southern blot hybridization, and named ERD (early-responsive todehydration) clones. Partial sequencing of the cDNA clones revealed that three ERDs were identical to those of HSP cognates (Athsp70-1, Athsp81-2, and ubiquitin extension protein). Dehydration stress strongly induced the expression of genes for the three ERDs, while application of ABA, which is known to act as a signal transmitter in dehydration-stressed plants, did not significantly affect the ERD gene expression. This result suggests that these HSP cognates are preferentially responsive to dehydration stress inA. thaliana, and that signaling pathways for the expression of these genes under conditions of dehydration stress are not mainly mediated by ABA. We also discuss the possible functions of these three ERD gene products against dehydration stress.     

Leucine-rich repeat receptor-like kinase1 is a key membrane-bound regulator of abscisic acid early signaling in Arabidopsis

Abscisic acid (ABA) is important in seed maturation, seed dormancy, stomatal closure, and stress response. Many genes that function in ABA signal transduction pathways have been identified. However, most important signaling molecules involved in the perception of the ABA signal or with ABA receptors have not been identified yet. Receptor-like kinase1 (RPK1), a Leu-rich repeat (LRR) receptor kinase in the plasma membrane, is upregulated by ABA in Arabidopsis thaliana. Here, we show the phenotypes of T-DNA insertion mutants and RPK1-antisense plants. Repression of RPK1 expression in Arabidopsis decreased sensitivity to ABA during germination, growth, and stomatal closure; microarray and RNA gel analysis showed that many ABA-inducible genes are downregulated in these plants. Furthermore, overexpression of the RPK1 LRR domain alone or fused with the Brassinosteroid-insensitive1 kinase domain in plants resulted in phenotypes indicating ABA sensitivity. RPK1 is involved in the main ABA signaling pathway and in early ABA perception in Arabidopsis.