Mitochondrial Porin Isoform AtVDAC1 Regulates the Competence of Arabidopsis thaliana to Agrobacterium-Mediated Genetic Transformation

Maize transcription factor ZmNAC2 enhances osmotic stress tolerance in transgenic Arabidopsis

Osmotic stress seriously limits crop yield and quality. Among plant-specific transcription factors families, the NAC family of transcription factors is extensively involved in various growth, development and stress responses. Here we identified a maize NAC family transcription factor ZmNAC2 with inducible gene expression in response to osmotic stress. The subcellular localization showed that it was localized in the nucleus and overexpression of ZmNAC2 in Arabidopsis significantly promoted seed germination and elevated cotyledon greening under osmotic stress. ZmNAC2 also enhanced stomatal closure and decreased water loss in transgenic Arabidopsis. Overexpression of ZmNAC2 activated ROS scavenging and the transgenic lines accumulated less MDA and developed more lateral roots with drought or mannitol treatment. Further RNA-seq and qRT-PCR analysis showed that ZmNAC2 up-regulated a number of genes related to osmotic stress resistance, as well as plant hormone signaling genes. All together, ZmNAC2 enhances osmotic stress tolerance by regulating multiple physiological processes and molecular mechanisms, and exhibits potential as the target gene in crop breeding to increase osmotic stress resistance.

Characterization of the voltage-dependent anion channel (VDAC) gene family in wheat (Triticum aestivum L.) and its potential mechanism in response to drought and salinity stresses

Voltage-dependent anion channels (VDACs) are major transport proteins localized in the outer membrane of mitochondria and play critical roles in regulating plant growth and responding to stress. In this study, a total of 26 VDAC genes in common wheat (Triticum aestivum L.) were identified. TaVDACs that contained β-barrel structures were classified into three groups with phylogenetic and sequence alignment. Additionally, the gene structure and protein conserved motif composition varied among diverse subfamilies but were relatively conserved within the same subfamily. The basic elements that were stress- and hormone-related, including TATA-box, CAAT-box, MBS, LTR, TC-rich repeats, ABRE, P-box and TATC-box, were predicted within the promoter region of TaVDAC genes. TaVDAC expression patterns differed among tissues, organs and abiotic stress conditions. Overexpression (OE) of TaVDAC1-B conferred high tolerance to salinity and less resistance to drought stress in Arabidopsis thaliana. TaVDAC1-B interacted with Nucleoredoxin-D1 (TaNRX-D1) protein. Furthermore, compared with WT lines, salinity stress further upregulated the level of AtNRX1 (homologous gene of TaNRX-D1 in Arabidopsis) expression and the activity of superoxide dismutase in TaVDAC1-B OE lines, which led to a decrease in superoxide radical accumulation; drought stress further downregulated AtNRX1 expression and superoxide dismutase activity in TaVDAC1-B OE lines, resulting in the accumulation of superoxide radicals. Our study not only presents comprehensive information for understanding the VDAC gene family in wheat but also proposes a potential mechanism in response to drought and salinity stress.

VDAC1 Negatively Regulates Floral Transition in Arabidopsis thaliana

Voltage-dependent anion channels (VDACs) are the most important proteins in mitochondria. They localize to the outer mitochondrial membrane and contribute to the metabolite transport between the mitochondria and cytoplasm, which aids plant growth regulation. Here, we report that Arabidopsis thaliana VDAC1 is involved in the floral transition, with the loss of AtVDAC1 function, resulting in an early-flowering phenotype. AtVDAC1 is expressed ubiquitously in Arabidopsis. To identify the flowering pathway integrators that may be responsible for AtVDAC1′s function during the floral transition, an RNA-seq analysis was performed. In total, 106 differentially expressed genes (DEGs) were identified between wild-type and atvdac1-5 mutant seedlings. However, none were involved in flowering-related pathways. In contrast, AtVDAC1 physically associated with FLOWERING LOCUS T. Thus, in the floral transition, AtVDAC1 may function partly through the FLOWERING LOCUS T protein.

Gametophytic Abortion in Heterozygotes but Not in Homozygotes: Implied Chromosome Rearrangement during T-DNA Insertion at the ASF1 Locus in Arabidopsis

T-DNA insertional mutations in Arabidopsis genes have conferred huge benefits to the research community, greatly facilitating gene function analyses. However, the insertion process can cause chromosomal rearrangements. Here, we show an example of a likely rearrangement following T-DNA insertion in the Anti-Silencing Function 1B (ASF1B) gene locus on Arabidopsis chromosome 5, so that the phenotype was not relevant to the gene of interest, ASF1B. ASF1 is a histone H3/H4 chaperone involved in chromatin remodeling in the sporophyte and during reproduction. Plants that were homozygous for mutant alleles asf1a or asf1b were developmentally normal. However, following self-fertilization of double heterozygotes (ASF1A/asf1a ASF1B/asf1b, hereafter AaBb), defects were visible in both male and female gametes. Half of the AaBb and aaBb ovules displayed arrested embryo sacs with functional megaspore identity. Similarly, half of the AaBb and aaBb pollen grains showed centromere defects, resulting in pollen abortion at the bi-cellular stage of the male gametophyte. However, inheritance of the mutant allele in a given gamete did not solely determine the abortion phenotype. Introducing functional ASF1B failed to rescue the AaBb- and aaBb- mediated abortion, suggesting that heterozygosity in the ASF1B gene causes gametophytic defects, rather than the loss of ASF1. The presence of reproductive defects in heterozygous mutants but not in homozygotes, and the characteristic all-or-nothing pollen viability within tetrads, were both indicative of commonly-observed T-DNA-mediated translocation activity for this allele. Our observations reinforce the importance of complementation tests in assigning gene function using reverse genetics.

Agrobacterium tumefaciens: A Bacterium Primed for Synthetic Biology

Agrobacterium tumefaciens is an important tool in plant biotechnology due to its natural ability to transfer DNA into the genomes of host plants. Genetic manipulations of A. tumefaciens have yielded considerable advances in increasing transformational efficiency in a number of plant species and cultivars. Moreover, there is overwhelming evidence that modulating the expression of various mediators of A. tumefaciens virulence can lead to more successful plant transformation; thus, the application of synthetic biology to enable targeted engineering of the bacterium may enable new opportunities for advancing plant biotechnology. In this review, we highlight engineering targets in both A. tumefaciens and plant hosts that could be exploited more effectively through precision genetic control to generate high-quality transformation events in a wider range of host plants. We then further discuss the current state of A. tumefaciens and plant engineering with regard to plant transformation and describe how future work may incorporate a rigorous synthetic biology approach to tailor strains of A. tumefaciens used in plant transformation.

Profiling of the Receptor for Activated C Kinase 1a (RACK1a) interaction network in Arabidopsis thaliana

As a scaffold protein, Receptor for Activated C Kinase 1a (RACK1) interacts with many proteins and is involved in multiple biological processes in Arabidopsis. However, the global RACK1 protein interaction network in higher plants remains poorly understood. Here, we generated a yeast two-hybrid library using mixed samples from different developmental stages of Arabidopsis thaliana. Using RACK1a as bait, we performed a comprehensive screening of the resulting library to identify RACK1a interactors at the whole-transcriptome level. We selected 1065 independent positive clones that led to the identification of 215 RACK1a interactors. We classified these interactors into six groups according to their potential functions. Several interactors were selected for bimolecular fluorescence complementation (BiFC) analysis and their interaction with RACK1a was confirmed in vivo. Our results provide further insight into the molecular mechanisms through which RACK1a regulates various growth and development processes in higher plants.

Comparative proteomics of two citrus varieties in response to infection by the fungus Alternaria alternata

Alternaria brown spot (ABS) is a disease caused by the necrotrophic fungus Alternaria alternata, which induces necrotic lesions on fruits and young leaves due to the production of the host-specific ACT toxin by the fungus. To better understand the citrus-A. alternata interaction and to identify putative resistance proteins, as well as the receptor of the ACT toxin, citrus plants susceptible ('Minneola' mandarin) and resistant ('Clemenules' tangor) to A. alternata, infected or not (control) with the pathogen were analyzed by proteomics. Protein changes were observed between citrus genotypes after infection, and 150 candidate proteins were obtained. A general scheme of the metabolic processes involved in susceptible and resistant citrus-A. alternata interactions was designed. Susceptible plants presented a high level of proteins involved in stress response at the final stages of the infection, whereas resistant plants presented high level of ROS proteins, metabolic proteins, and proteins involved in the immune system process. Proteins like ferredoxin and cyclophilin are specific to the susceptible variety and may be good candidates as fungal effector-interacting proteins. This is the first citrus-A. alternata proteomics analysis, which has allowed a better understanding of the molecular bases of the citrus response to ABS disease.