Modifying the Expression of Cysteine Protease Gene PCP Affects Pollen Development, Germination and Plant Drought Tolerance in Maize.

Cysteine proteases (CPs) are vital proteolytic enzymes that play critical roles in various plant processes. However, the particular functions of CPs in maize remain largely unknown. We recently identified a pollen-specific CP (named PCP), which highly accumulated on the surface of maize pollen. Here, we reported that PCP played an important role in pollen germination and drought response in maize. Overexpression of PCP inhibited pollen germination, while mutation of PCP promoted pollen germination to some extent. Furthermore, we observed that germinal apertures of pollen grains in the PCP-overexpression transgenic lines were excessively covered, whereas this phenomenon was not observed in the wild type (WT), suggesting that PCP regulated pollen germination by affecting the germinal aperture structure. In addition, overexpression of PCP enhanced drought tolerance in maize plants, along with the increased activities of the antioxidant enzymes and the decreased numbers of the root cortical cells. Conversely, mutation of PCP significantly impaired drought tolerance. These results may aid in clarifying the precise functions of CPs in maize and contribute to the development of drought-tolerant maize materials.

Cadmium tolerance and hyperaccumulation in plants - A proteomic perspective of phytoremediation.

Cadmium (Cd) is a major environmental pollutant and poses a risk of transfer into the food chain through contaminated plants. Mechanisms underlying Cd tolerance and hyperaccumulation in plants are not fully understood. Proteomics-based approaches facilitate an in-depth understanding of plant responses to Cd stress at the systemic level by identifying Cd-inducible differentially abundant proteins (DAPs). In this review, we summarize studies related to proteomic changes associated with Cd-tolerance mechanisms in Cd-tolerant crops and Cd-hyperaccumulating plants, especially the similarities and differences across plant species. The enhanced DAPs identified through proteomic studies can be potential targets for developing Cd-hyperaccumulators to remediate Cd-contaminated environments and Cd-tolerant crops with low Cd content in the edible organs. This is of great significance for ensuring the food security of an exponentially growing global population. Finally, we discuss the methodological drawbacks in current proteomic studies and propose that better protocols and advanced techniques should be utilized to further strengthen the reliability and applicability of future Cd-stress-related studies in plants. This review provides insights into the improvement of phytoremediation efficiency and an in-depth study of the molecular mechanisms of Cd enrichment in plants.

Quaternary ammonium iminofullerenes improve root growth of oxidative-stress maize through ASA-GSH cycle modulating redox homeostasis of roots and ROS-mediated root-hair elongation.

BACKGROUND: Various environmental factors are capable of oxidative stress to result in limiting plant development and agricultural production. Fullerene-based carbon nanomaterials can enable radical scavenging and positively regulate plant growth. Even so, to date, our knowledge about the mechanism of fullerene-based carbon nanomaterials on plant growth and response to oxidative stress is still unclear. RESULTS: 20 or 50 mg/L quaternary ammonium iminofullerenes (IFQA) rescued the reduction in root lengths and root-hair densities and lengths of Arabidopsis and maize induced by accumulation of endogenous hydrogen peroxide (H2O2) under 3-amino-1,2,4-triazole or exogenous H2O2 treatment, as well as the root active absorption area and root activity under exogenous H2O2 treatment. Meanwhile, the downregulated contents of ascorbate acid (ASA) and glutathione (GSH) and the upregulated contents of dehydroascorbic acid (DHA), oxidized glutathione (GSSG), malondialdehyde (MDA), and H2O2 indicated that the exogenous H2O2 treatment induced oxidative stress of maize. Nonetheless, application of IFQA can increase the ratios of ASA/DHA and GSH/GSSG, as well as the activities of glutathione reductase, and ascorbate peroxidase, and decrease the contents of H2O2 and MDA. Moreover, the root lengths were inhibited by buthionine sulfoximine, a specific inhibitor of GSH biosynthesis, and subsequently rescued after addition of IFQA. The results suggested that IFQA could alleviate exogenous-H2O2-induced oxidative stress on maize by regulating the ASA-GSH cycle. Furthermore, IFQA reduced the excess accumulation of ROS in root hairs, as well as the NADPH oxidase activity under H2O2 treatment. The transcript levels of genes affecting ROS-mediated root-hair development, such as RBOH B, RBOH C, PFT1, and PRX59, were significantly induced by H2O2 treatment and then decreased after addition of IFQA. CONCLUSION: The positive effect of fullerene-based carbon nanomaterials on maize-root-hair growth under the induced oxidative stress was discovered. Application IFQA can ameliorate oxidative stress to promote maize-root growth through decreasing NADPH-oxidase activity, improving the scavenging of ROS by ASA-GSH cycle, and regulating the expressions of genes affecting maize-root-hair development. It will enrich more understanding the actual mechanism of fullerene-based nanoelicitors responsible for plant growth promotion and protection from oxidative stress.

Genome-Wide Identification and Comparison of Cysteine Proteases in the Pollen Coat and Other Tissues in Maize.

Cysteine proteases, belonging to the C1-papain family, play a major role in plant growth and development, senescence, and immunity. There is evidence to suggest that pollen cysteine protease (CP) (ZmCP03) is involved in regulating the anther development and pollen formation in maize. However, there is no report on the genome-wide identification and comparison of CPs in the pollen coat and other tissues in maize. In this study, a total of 38 homologous genes of ZmCP03 in maize were identified. Subsequently, protein motifs, conserved domains, gene structures, and duplication patterns of 39 CPs are analyzed to explore their evolutionary relationship and potential functions. The cis-elements were identified in the upstream sequence of 39 CPs, especially those that are related to regulating growth and development and responding to environmental stresses and hormones. The expression patterns of these genes displayed remarked difference at a tissue or organ level in maize based on the available transcriptome data in the public database. Quantitative reverse transcription PCR (RT-qPCR) analysis showed that ZmCP03 was preferably expressed at a high level in maize pollen. Analyses by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot, immunofluorescence and immunogold electron microscopy all validated the cellular localization of ZmCP03 in both the pollen coat and pollen cytoplasm. In addition, 142 CP genes from Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa) and cotton (Gossypium hirsutum), together with 39 maize CPs, were retrieved to analyze their evolution by comparing with orthologous genes. The results suggested that ZmCP03 was relatively conservative and stable during evolution. This study may provide a referential evidence on the function of ZmCP03 in pollen development and germination in maize.

Quaternary ammonium iminofullerenes promote root growth and osmotic-stress tolerance in maize via ROS neutralization and improved energy status.

In the present study, the role of quaternary ammonium iminofullerenes (IFQA) on the root growth of plant seedlings was investigated. The root elongation of Arabidopsis and maize exposed to 20 and 50 mg/L of IFQA was promoted under normal and osmotic stress conditions, respectively. In the meantime, the root active absorption area and adenosine triphosphate content in roots of maize seedlings were enhanced by IFQA treatment, however, the contents of hydrogen peroxide (H2O2) and malondialdehyde in roots were down-regulated. IFQA application improved glutathione transferase and glutathione reductase activities and the ratios of glutathione/oxidized glutathione and ascorbic acid/dehydroascorbic acid, and restored the inhibition of root elongation caused by the excess accumulation of H2O2 in roots of maize seedlings under osmotic stress. Furthermore, the expression of 14 proteins involved in cell growth, energy metabolism, and stress response in maize roots was upregulated by two-dimensional electrophoresis combined with mass spectrometry. This analysis revealed that IFQA stimulated the redox pathway to maintain balance levels of reactive oxygen species to ensure normal cell metabolism, promote energy production for root growth, and enhance osmotic-stress tolerance. It provided crucial information to elucidate the mechanism of the root growth of crop seedlings enhanced by water-soluble fullerene-based nanomaterials.

A new adenylyl cyclase, putative disease-resistance RPP13-like protein 3, participates in abscisic acid-mediated resistance to heat stress in maize.

In plants, 3´,5´-cyclic adenosine monophosphate (cAMP) is an important second messenger with varied functions; however, only a few adenylyl cyclases (ACs) that synthesize cAMP have been identified. Moreover, the biological roles of ACs/cAMP in response to stress remain largely unclear. In this study, we used quantitative proteomics techniques to identify a maize heat-induced putative disease-resistance RPP13-like protein 3 (ZmRPP13-LK3), which has three conserved catalytic AC centres. The AC activity of ZmRPP13-LK3 was confirmed by in vitro enzyme activity analysis, in vivo RNAi experiments, and functional complementation in the E. coli cyaA mutant. ZmRPP13-LK3 is located in the mitochondria. The results of in vitro and in vivo experiments indicated that ZmRPP13-LK3 interacts with ZmABC2, a possible cAMP exporter. Under heat stress, the concentrations of ZmRPP13-LK3 and cAMP in the ABA-deficient mutant vp5 were significantly less than those in the wild-type, and treatment with ABA and an ABA inhibitor affected ZmRPP13-LK3 expression in the wild-type. Application of 8-Br-cAMP, a cAMP analogue, increased heat-induced expression of heat-shock proteins in wild-type plants and alleviated heat-activated oxidative stress. Taken together, our results indicate that ZmRPP13-LK3, a new AC, can catalyse ATP for the production of cAMP and may be involved in ABA-regulated heat resistance.

[Characterization and expression analysis of two cotton genes encoding putative UDP-Glycosyltransferases].

UDP-Glycosyltransferases (UGT) are a large family of enzymes, which catalyze the transfer of a sugar from an activated sugar donor to an acceptor molecule. Both in plant and in mammalian, they are important in maintenance of cellular homeostasis. In this study, two genes (designated GhUGT1 and GhUGT2, respectively) encoding putative UGT were isolated from cotton fiber cDNA library. The deduced proteins contain the signature sequences of plant UGTs in the C-terminal region. The GhUGT1 gene encodes a polypeptide of 457 amino acids, and displays homology at amino acid levels with the known glucosyltransferase genes. Sequence analysis revealed that the GhUGT2 merely encodes a small protein, as there is a nucleotide substitution that results in formation of a stop codon in its open-reading frame. Real-time RT-PCR analysis revealed that the expression of GhUGT1 is higher in the fast growth tissues, such as in fibers and roots. GhUGT2 has also higher expression in roots, but with lower expression levels in fibers and other tissues. The result also showed that the expression of GhUGT1 is higher than GhUGT2. Further study showed that GhUGT1 and GhUGT2 expressions are regulated under osmotic stress, suggesting they may be involved in plants responding to osmotic stress.