Many trace metals are essential micronutrients, but also potent toxins. Due to natural and anthropogenic causes, vastly different trace metal concentrations occur in various habitats, ranging from deficient to toxic levels. Therefore, one focus of plant research is on the response to trace metals in terms of uptake, transport, sequestration, speciation, physiological use, deficiency, toxicity, and detoxification. In this review, we cover most of these aspects for the essential micronutrients copper, iron, manganese, molybdenum, nickel, and zinc to provide a broader overview than found in other recent reviews, to cross-link aspects of knowledge in this very active research field that are often seen in a separated way. For example, individual processes of metal usage, deficiency, or toxicity often were not mechanistically interconnected. Therefore, this review also aims to stimulate the communication of researchers following different approaches, such as gene expression analysis, biochemistry, or biophysics of metalloproteins. Furthermore, we highlight recent insights, emphasizing data obtained under physiologically and environmentally relevant conditions.

Trace metal metabolism in plants.

Single-nucleus RNA and ATAC sequencing reveals the impact of chromatin accessibility on gene expression in Arabidopsis roots at the single-cell level.

Increasing grain yield is the most important object of crop breeding. Here, we report that the elevated expression of a conserved microRNA, OsmiR408, could positively regulate grain yield in rice (Oryza sativa) by increasing panicle branches and grain number. We further showed that OsmiR408 regulates grain yield by down-regulating its downstream target, OsUCL8, which is an uclacyanin (UCL) gene of the phytocyanin family. The knock down or knock out of OsUCL8 also increases grain yield, while the overexpression of OsUCL8 results in an opposite phenotype. Spatial and temporal expression analyses showed that OsUCL8 was highly expressed in pistils, young panicles, developing seeds, and inflorescence meristem and was nearly complementary to that of OsmiR408. Interestingly, the OsUCL8 protein was localized to the cytoplasm, distinct from a majority of phytocyanins, which localize to the plasma membrane. Further studies revealed that the cleavage of OsUCL8 by miR408 affects copper homeostasis in the plant cell, which, in turn, affects the abundance of plastocyanin proteins and photosynthesis in rice. To our knowledge, this is the first report of the effects of miR408-OsUCL8 in regulating rice photosynthesis and grain yield. Our study further broadens the perspective of microRNAs and UCLs and provides important information for breeding high-yielding crops through genetic engineering.

MiR408 Regulates Grain Yield and Photosynthesis via a Phytocyanin Protein.

Plants have evolved multifaceted defence mechanisms to resist pathogen infection. Production of the pathogenesis-related (PR) proteins in response to pathogen attack has been implicated in plant disease resistance specialized in systemic-acquired resistance (SAR). Our earlier studies have reported that a full length TaLr35PR5 gene, encoding a protein exhibiting amino acid and structural similarity to a sweet protein thaumatin, was isolated from wheat near-isogenic line TcLr35. The present study aims to understand the function of TaLr35PR5 gene in Lr35-mediated adult resistance to Puccinia triticina. We determined that the TaLr35PR5 protein contained a functional secretion peptide by utilizing the yeast signal sequence trap system. Using a heterologous expression assay on onion epidermal cells we found that TaLr35PR5 protein was secreted into the apoplast of onion cell. Expression of TaLr35PR5 was significantly reduced in BSMV-induced gene silenced wheat plants, and pathology test on these silenced plants revealed that Lr35-mediated resistance phenotype was obviously altered, indicating that Lr35-mediated resistance was compromised. All these findings strongly suggest that TaLr35PR5 is involved in Lr35-mediated adult wheat defense in response to leaf rust attack.

/pdf/functional-analysis-of-a-pathogenesis-related-thaumatin-like-1u518eqh61.pdf

Functional analysis of a pathogenesis-related thaumatin-like protein gene TaLr35PR5 from wheat induced by leaf rust fungus.

The migration of cadmium (Cd) from contaminated soil to rice is a cause for concern. However, the molecular mechanism underlying the response of rice roots to various Cd stresses remains to be clarified from the viewpoint of the co-expression network at a system-wide scale. We employed a comparative RNAseq-based approach to identify early Cd-responsive differentially expressed genes (DEGs) in rice ‘Nipponbare’ seedling roots after 1 h of high-Cd treatment. A multiplicity of the identified 1772 DEGs were implicated in hormone signaling and transcriptional regulation, particularly NACs and WRKYs were all upregulated under Cd stress. All of the 6 Cd-upregulated ABC transporters were pleiotropic drug resistance proteins (PDRs), whereas all of the 6 ZRT/IRT-like proteins (ZIPs) were consistently downregulated by Cd treatment. To further confirm our results of this early transcriptomic response to Cd exposure, we then conducted weighted gene co-expression network analysis (WGCNA) to re-analyze our RNAseq data in combination with other 11 previously published RNAseq datasets for rice roots exposed to diverse concentrations of Cd for extended treatment periods. This integrative approach identified 271 transcripts as universal Cd-regulated DEGs that are key components of the Cd treatment coupled co-expression module. A global view of the 164 transcripts with annotated functions in pathway networks revealed several Cd-upregulated key functional genes, including transporter ABCG36/OsPDR9, 12-oxo-phytodienoic acid reductases (OPRs) for JA synthesis, and ZIM domain proteins JAZs in JA signaling, as well as OsWRKY10, NAC, and ZFP transcription factors. More importantly, 104 of these, including ABCG36/OsPDR9, OsNAC3, as well as several orthologs in group metalloendoproteinase, plastocyanin-like domain containing proteins and pectin methylesterase inhibitor, may respond specifically to various Cd pressures, after subtracting the 60 general stress-responsive genes reported to be commonly upregulated following multiple stresses. An integrative approach was implemented to identify DEGs and co-expression network modules in response to various Cd pressures, and 104 of the 164 annotatable universal Cd-responsive DEGs may specifically respond to various Cd pressures. These results provide insight into the universal molecular mechanisms beneath the Cd response in rice roots, and suggest many promising targets for improving the rice acclimation process against Cd toxicity.

/pdf/co-expression-network-analysis-of-the-transcriptomes-of-rice-1nj3xgyopp.pdf

Co-expression network analysis of the transcriptomes of rice roots exposed to various cadmium stresses reveals universal cadmium-responsive genes.

Sclerotinia sclerotiorum (Lib.) de Bary is an unusual pathogen which has the broad host range, diverse infection modes, and potential double feeding lifestyles of both biotroph and necrotroph. It is capable of infecting over 400 plant species found worldwide and more than 60 names have agriculturally been used to refer to diseases caused by this pathogen. Plant defense to S. sclerotiorum is a complex biological process and exhibits a typical quantitative disease resistance (QDR) response. Recent studies using Arabidopsis thaliana and crop plants have obtained new advances in mechanisms used by plants to cope with S. sclerotiorum infection. In this review, we focused on our current understanding on plant defense mechanisms against this pathogen, and set up a model for the defense process including three stages: recognition of this pathogen, signal transduction and defense response. We also have a particular interest in defense signaling mediated by diverse signaling molecules. We highlight the current challenges and unanswered questions in both the defense process and defense signaling. Essentially, we discussed candidate resistance genes newly mapped by using high-throughput experiments in important crops, and classified these potential gene targets into different stages of the defense process, which will broaden our understanding of the genetic architecture underlying quantitative resistance to S. sclerotiorum. We proposed that more powerful mapping population(s) will be required for accurate and reliable QDR gene identification.

/pdf/recent-advances-in-mechanisms-of-plant-defense-to-oazw3xrych.pdf

Recent Advances in Mechanisms of Plant Defense to Sclerotinia sclerotiorum.

Summary
Brassica napus L. is an important oil crop worldwide, and is the main raw material for biofuel. Seed weight and seed size are the main contributors to seed yield. DA1 (DA means big in Chinese) is an ubiquitin receptor and negatively regulates seed size. Down-regulation of AtDA1 in Arabidopsis leads to larger seeds and organs by increasing cell proliferation in integuments. In this study, BnDA1was down-regulated in B. napus by over expressed of AtDA1R358K, which is a functional deficiency of DA1 with an arginine-to-lysine mutation at the 358th amino acid. The results showed that the biomass and size of the seeds, cotyledons, leaves, flowers, and siliques of transgenic plants all increased significantly. Especially, the 1000 seed weight increased 21.23% and the seed yield per plant increased 13.22% in field condition. The transgenic plants had no negative traits related to yield. The candidate gene association analysis demonstrated that the BnDA1 locus was contributed to the seeds weight. Therefore, our study showed that regulation of DA1 in B. napus can increase the seed yield and biomass, and DA1 is a promising target for crop improvement.

This article is protected by copyright. All rights reserved.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/pbi.12696

Down-regulation of BnDA1, whose gene locus is associated with the seeds weight, improves the seeds weight and organ size in Brassica napus.

Thaumatin-like protein (TLP) is one of pathogenesis-related protein family, which plays an important role in plant defense system. While its origin and expansion is unknown in plants. Here, we investigated the evolution of this gene family by performing a genome-wide identification and comparison in Arabidopsis, Oryza, Populus, Zea, Physcomitrella and Chlamydomonas. We found a birth process of this gene family in evolution. Tandem and segmental duplication played dominant roles for their expansion. In addition, TLPs were under purifying selection, and most members were responding to some biotic or abiotic stresses. Functional network analysis exhibited some resistance genes working together with TLPs. Our findings shed some light on this family gene evolution in plants, which might provide a base for further functional investigation of this family.

Expansion and evolution of thaumatin-like protein (TLP) gene family in six plants

Phytocyanins (PCs) are plant-specific blue copper proteins, which play essential roles in electron transport. While the origin and expansion of this gene family is not well-investigated in plants. Here, we investigated their evolution by undertaking a genome-wide identification and comparison in 10 plants: Arabidopsis, rice, poplar, tomato, soybean, grape, maize, Selaginella moellendorffii, Physcomitrella patens, and Chlamydomonas reinhardtii. We found an expansion process of this gene family in evolution. Except PCs in Arabidopsis and rice, which have described in previous researches, a structural analysis of PCs in other eight plants indicated that 292 PCs contained N-terminal secretion signals and 217 PCs were expected to have glycosylphosphatidylinositol-anchor signals. Moreover, 281 PCs had putative arabinogalactan glycomodules and might be AGPs. Chromosomal distribution and duplication patterns indicated that tandem and segmental duplication played dominant roles for the expansion of PC genes. In addition, gene organization and motif compositions are highly conserved in each clade. Furthermore, expression profiles of maize PC genes revealed diversity in various stages of development. Moreover, all nine detected maize PC genes (ZmUC10, ZmUC16, ZmUC19, ZmSC2, ZmUC21, ZmENODL10, ZmUC22, ZmENODL13, and ZmENODL15) were down-regulated under salt treatment, and five PCs (ZmUC19, ZmSC2, ZmENODL10, ZmUC22, and ZmENODL13) were down-regulated under drought treatment. ZmUC16 was strongly expressed after drought treatment. This study will provide a basis for future understanding the characterization of this family.

/pdf/comparative-analysis-of-the-phytocyanin-gene-family-in-10-4mckye2xie.pdf

Comparative analysis of the phytocyanin gene family in 10 plant species: a focus on Zea mays

GDSL lipases form multigene families in Arabidopsis, rice and some other sequenced plant species. Unlike classical GxSxG motif-containing lipases, this new sub-family of lipolytic enzymes possesses a GDSL sequence motif (GDSxxDxG), and members are active in the hydrolysis and synthesis of a variety of lipids. Research on plant GDSL lipases started later than studies of microbial and animal GDSL lipases; therefore, our knowledge regarding plant GDSL lipases, from sequences to functional mechanisms, is limited. Recently, some GDSL lipase genes have been cloned and identified in different plant species. In this paper, we present a comprehensive review of the advances in research on plant GDSL lipases, which include their structures, distributions, biochemical activities, expression patterns and biological functions. Plant GDSL lipases have very flexible enzyme active sites, which can lead to extensive substrate binding and result in multifunctional properties. They play important roles in many physiological and biochemical processes, such as plant growth and development, organ morphogenesis, adversity stress and lipid metabolism. In addition, their potential applications in agriculture and industry are discussed.

Li-Na Ding

Papers

Recent Advances in Mechanisms of Plant Defense to Sclerotinia sclerotiorum.

Down-regulation of BnDA1, whose gene locus is associated with the seeds weight, improves the seeds weight and organ size in Brassica napus.

Expansion and evolution of thaumatin-like protein (TLP) gene family in six plants

Comparative analysis of the phytocyanin gene family in 10 plant species: a focus on Zea mays

Advances in plant GDSL lipases: from sequences to functional mechanisms