The G-Protein ß Subunit AGB1 Promotes Hypocotyl Elongation through Inhibiting Transcription Activation Function of BBX21 in Arabidopsis.

Hypocotyl development in Arabidopsis thaliana is regulated by light and endogenous hormonal cues, making it an ideal model to study the interplay between light and endogenous growth regulators. BBX21, a B-box (BBX)-like zinc-finger transcription factor, integrates light and abscisic acid signals to regulate hypocotyl elongation in Arabidopsis. Heterotrimeric G-proteins are pivotal regulators of plant development. The short hypocotyl phenotype of the G-protein ß-subunit (AGB1) mutant (agb1-2) has been previously identified, but the precise role of AGB1 in hypocotyl elongation remains enigmatic. Here, we show that AGB1 directly interacts with BBX21, and the short hypocotyl phenotype of agb1-2 is partially suppressed in agb1-2bbx21-1 double mutant. BBX21 functions in the downstream of AGB1 and overexpression of BBX21 in agb1-2 causes a more pronounced reduction in hypocotyl length, indicating that AGB1 plays an oppositional role in relation to BBX21 during hypocotyl development. Furthermore, we demonstrate that the C-terminal region of BBX21 is important for both its intracellular localization and its transcriptional activation activity that is inhibited by interaction with AGB1. ChIP assays showed that BBX21 specifically associates with its own promoter and with those of BBX22, HY5, and GA2ox1. which is not altered in agb1-2. These data suggest that the AGB1-BBX21 interaction only affects the transcriptional activation activity of BBX21 but has no effect on its DNA binding ability. Taken together, our data demonstrate that AGB1 positively promotes hypocotyl elongation through repressing BBX21 activity.

A G-protein ß subunit, AGB1, negatively regulates the ABA response and drought tolerance by down-regulating AtMPK6-related pathway in Arabidopsis.

Heterotrimeric G-proteins are versatile regulators involved in diverse cellular processes in eukaryotes. In plants, the function of G-proteins is primarily associated with ABA signaling. However, the downstream effectors and the molecular mechanisms in the ABA pathway remain largely unknown. In this study, an AGB1 mutant (agb1-2) was found to show enhanced drought tolerance, indicating that AGB1 might negatively regulate drought tolerance in Arabidopsis. Data showed that AGB1 interacted with protein kinase AtMPK6 that was previously shown to phosphorylate AtVIP1, a transcription factor responding to ABA signaling. Our study found that transcript levels of three ABA responsive genes, AtMPK6, AtVIP1 and AtMYB44 (downstream gene of AtVIP1), were significantly up-regulated in agb1-2 lines after ABA or drought treatments. Other ABA-responsive and drought-inducible genes, such as RD29A (downstream gene of AtMYB44), were also up-regulated in agb1-2 lines. Furthermore, overexpression of AtVIP1 resulted in hypersensitivity to ABA at seed germination and seedling stages, and significantly enhanced drought tolerance in transgenic plants. These results suggest that AGB1 was involved in the ABA signaling pathway and drought tolerance in Arabidopsis through down-regulating the AtMPK6, AtVIP1 and AtMYB44 cascade.

ABI-like transcription factor gene TaABL1 from wheat improves multiple abiotic stress tolerances in transgenic plants.

The phytohormone abscisic acid (ABA) plays crucial roles in adaptive responses of plants to abiotic stresses. ABA-responsive element binding proteins (AREBs) are basic leucine zipper transcription factors that regulate the expression of downstream genes containing ABA-responsive elements (ABREs) in promoter regions. A novel ABI-like (ABA-insensitive) transcription factor gene, named TaABL1, containing a conserved basic leucine zipper (bZIP) domain was cloned from wheat. Southern blotting showed that three copies were present in the wheat genome. Phylogenetic analyses indicated that TaABL1 belonged to the AREB subfamily of the bZIP transcription factor family and was most closely related to ZmABI5 in maize and OsAREB2 in rice. Expression of TaABL1 was highly induced in wheat roots, stems, and leaves by ABA, drought, high salt, and low temperature stresses. TaABL1 was localized inside the nuclei of transformed wheat mesophyll protoplast. Overexpression of TaABL1 enhanced responses of transgenic plants to ABA and hastened stomatal closure under stress, thereby improving tolerance to multiple abiotic stresses. Furthermore, overexpression of TaABL1 upregulated or downregulated the expression of some stress-related genes controlling stomatal closure in transgenic plants under ABA and drought stress conditions, suggesting that TaABL1 might be a valuable genetic resource for transgenic molecular breeding.

W55a encodes a novel protein kinase that is involved in multiple stress responses.

Protein kinases play crucial roles in response to external environment stress signals. A putative protein kinase, W55a, belonging to SNF1-related protein kinase 2 (SnRK2) subfamily, was isolated from a cDNA library of drought-treated wheat seedlings. The entire length of W55a was obtained using rapid amplification of 5' cDNA ends (5'-RACE) and reverse transcription-polymerase chain reaction(RT-PCR). It contains a 1,029 -bp open reading frame (ORF) encoding 342 amino acids. The deduced amino acid sequence of W55a had eleven conserved catalytic subdomains and one Ser/Thr protein kinase active-site that characterize Ser/Thr protein kinases. Phylogenetic analysis showed that W55a was 90.38% homologous with rice SAPK1, a member of the SnRK2 family. Using nullisomic-tetrasomic and ditelocentric lines of Chinese Spring, W55a was located on chromosome 2BS. Expression pattern analysis revealed that W55a was upregulated by drought and salt, exogenous abscisic acid, salicylic acid, ethylene and methyl jasmonate, but was not responsive to cold stress. In addition, W55a transcripts were abundant in leaves, but not in roots or stems, under environmental stresses. Transgenic Arabidopsis plants overexpressing W55a exhibited higher tolerance to drought. Based on these findings, W55a encodes a novel dehydration-responsive protein kinase that is involved in multiple stress signal transductions.

[Maize transformation using xylose isomerase gene as a selection marker].

The xylA gene, encoding xylose isomerase, was cloned as a 1342-bp BamHI/SacI fragment from the E. coli. As a selection marker, the xylA gene was fused between the enhanced CaMV 35S promoter (E35S) and terminator (35St) in pBAC413 (Fig.2). pBAC413 was constructed to prevent the expression of sbeIIb in maize. PDS1000/He was used to bombard maize calli, which were induced to form by the elite inbred lines. The selection was carried out on the media containing concentrations of xylose from 0 to 100%. The results showed that the media containing 50% to 100% D-xylose were better, but differed with the genotype of maize (Tables 1 and 2). Successful integration of xylA gene into the maize genome was confirmed by DNA dot blotting, PCR and PCR-Southern hybridization (Figs.4 to 6). A method was established in which transformed maize cells were successively screened on a medium containing xylose instead of antibiotic and herbicide for bio-safety.

[Molecular basic of interaction between disease resistance gene and avirulence gene].

Plant-pathogen interaction is the more important phytopathological subjects. Landmark progress in the past 10 years have resulted in the identification of functional R genes from the host and Avr genes from the pathogen,additionally interaction between their encoded productions. This paper reviewed the two models of R-Avr interaction, namely "receptor-ligand model" and "guard model", and discussed how to utilize the R gene during crop breeding and commercial production.

Patterned growth of ZnO nanorod arrays on a large-area stainless steel grid.

Large-area ZnO nanorod arrays have been synthesized successfully on a stainless steel grid at a mild growth temperature of around 400 degrees C. The as-grown ZnO nanorods have uniform diameters of about 30-50 nm with approximately 5 nm tips. Patterned growth can be realized by engineering the shape of the grid in the growth. Photoluminescence demonstrates a sharp strong UV peak and a broad green band. The growth method provides a promising way of producing nanorod arrays with good controllability in patterns and morphologies, which will be critical in potential application such as high-efficiency filtering and catalysts.