Summary
Drought, a primary abiotic stress, seriously affects plant growth and productivity. Stomata play a vital role in regulating gas exchange and drought adaptation. However, limited knowledge ...exists of the molecular mechanisms underlying stomatal movement in trees. Here, PeCHYR1, a ubiquitin E3 ligase, was isolated from Populus euphratica, a model of stress adaptation in forest trees. PeCHYR1 was preferentially expressed in young leaves and was significantly induced by ABA (abscisic acid) and dehydration treatments. To study the potential biological functions of PeCHYR1, transgenic poplar 84K (Populus alba × Populus glandulosa) plants overexpressing PeCHYR1 were generated. PeCHYR1 overexpression significantly enhanced H2O2 production and reduced stomatal aperture. Transgenic lines exhibited increased sensitivity to exogenous ABA and greater drought tolerance than that of WT (wild‐type) controls. Moreover, up‐regulation of PeCHYR1 promoted stomatal closure and decreased transpiration, resulting in strongly elevated WUE (water use efficiency). When exposed to drought stress, transgenic poplar maintained higher photosynthetic activity and biomass accumulation. Taken together, these results suggest that PeCHYR1 plays a crucial role in enhancing drought tolerance via ABA‐induced stomatal closure caused by hydrogen peroxide (H2O2) production in transgenic poplar plants.
Summary
The regulatory framework of leaf senescence is gradually becoming clearer; however, the fine regulation of this process remains largely unknown.
Here, genetic analysis revealed that U2 small ...nuclear ribonucleoprotein B (U2B″), a component of the spliceosome, is a negative regulator of leaf senescence. Mutation of U2B″ led to precocious leaf senescence, whereas overexpression of U2B″ extended leaf longevity. Transcriptome analysis revealed that the jasmonic acid (JA) signaling pathway was activated in the u2b″ mutant. U2B″ enhances the generation of splicing variant JASMONATE ZIM‐DOMAIN 9β (JAZ9β) with an intron retention in the Jas motif, which compromises its interaction with CORONATINE INSENSITIVE1 and thus enhances the stability of JAZ9β protein. Moreover, JAZ9β could interact with MYC2 and obstruct its activity, thereby attenuating JA signaling. Correspondingly, overexpression of JAZ9β rescued the early senescence phenotype of the u2b″ mutant.
Furthermore, JA treatment promoted expression of U2B″ that was found to be a direct target of MYC2. Overexpression of MYC2 in the u2b″ mutant resulted in a more pronounced premature senescence than that in wild‐type plants.
Collectively, our findings reveal that the spliceosomal protein U2B″ fine‐tunes leaf senescence by enhancing the expression of JAZ9β and thereby attenuating JA signaling.
Electrical conductivity and dielectric parameters are general inherent features of materials. Controlling these characteristics through applied bias will add a new dimension to regulate the dynamic ...response of smart materials. Here, a fascinating electrical transport behavior is observed in topological insulator (TI) Bi2Te3 nanorods, which will play a vital role in intelligent materials or devices as a unit for information reception, processing or feedback. The Bi2Te3 nanorod aggregates exhibit a monotonic resistance response to voltage, with observed four‐fold change of electrical conductivity in a small range electric field of 1 V mm−1. The dielectric constant and dielectric loss of Bi2Te3 nanorod composites also show strong dependences on bias voltage due to the unique electrical transport characteristics. The unique voltage‐controlled electrical responses are attributed to the change of Fermi levels within the band structure of disordered TI nanorods, which are non‐parallel to the applied electric field. The excellent controllable inherent characteristics through electric field endows Bi2Te3 nanomaterials bright prospects for applications in smart devices and resistive random access memories.
Bi2Te3 nanorods exhibit monotonic resistance response to voltage and strong dependence of dielectric constant on voltage. Compared with other materials, the Bi2Te3 nanorod aggregates have the largest electrical conductivity variation range with smallest voltage scope. The fascinating electrical transport behavior endows the material with tremendous application potential in communication systems, smart devices, miniature generators, and intelligent storage.
Leaf senescence is an orderly process regulated by multiple internal factors and diverse environmental stresses including nutrient deficiency. Histone variants are involved in regulating plant growth ...and development. However, their functions and underlying regulatory mechanisms in leaf senescence remain largely unclear. Here, we found that H2B histone variant HTB4 functions as a negative regulator of leaf senescence. Loss of function of HTB4 led to early leaf senescence phenotypes that were rescued by functional complementation. RNA-seq analysis revealed that several Ib subgroup basic helix-loop-helix (bHLH) transcription factors (TFs) involved in iron (Fe) homeostasis, including bHLH038, bHLH039, bHLH100, and bHLH101, were suppressed in the htb4 mutant, thereby compromising the expressions of FERRIC REDUCTION OXIDASE 2 (FRO2) and IRON-REGULATED TRANSPORTER (IRT1), two important components of the Fe uptake machinery. Chromatin immunoprecipitation-quantitative polymerase chain reaction analysis revealed that HTB4 could bind to the promoter regions of Ib bHLH TFs and enhance their expression by promoting the enrichment of the active mark H3K4me3 near their transcriptional start sites. Moreover, overexpression of Ib bHLH TFs or IRT1 suppressed the premature senescence phenotype of the htb4 mutant. Our work established a signaling pathway, HTB4-bHLH TFs-FRO2/IRT1-Fe homeostasis, which regulates the onset and progression of leaf senescence.
Populus euphratica is the only arboreal species that is established in the world's largest shifting‐sand desert in China and is well‐adapted to the extreme desert environment, so it is widely ...considered a model system for researching into abiotic stress resistance of woody plants. However, few P. euphratica reference genes (RGs) have been identified for quantitative real‐time polymerase chain reaction (qRT‐PCR) until now. Validation of suitable RGs is essential for gene expression normalization research. In this study, we screened 16 endogenous candidate RGs in P. euphratica leaves in six abiotic stress treatments, including abscisic acid (ABA), cold, dehydration, drought, short‐duration salt (SS) and long‐duration salt (LS) treatments, each with 6 treatment gradients. After calculation of PCR efficiencies, three different software tools, NormFinder, geNorm and BestKeeper, were employed to analyze the qRT‐PCR data systematically, and the outputs were merged by means of a non‐weighted unsupervised rank aggregation method. The genes selected as optimal for gene expression analysis of the six treatments were RPL17 (ribosomal protein L17) in ABA, EF1α (elongation factor‐1 alpha) in cold, HIS (histone superfamily protein H3) in dehydration, GIIα in drought and SS, and TUB (tubulin) in LS. The expression of 60S (the 60S ribosomal protein) varied the least during all treatments. To illustrate the suitability of these RGs, the relative quantifications of three stress‐inducible genes, PePYL1, PeSCOF‐1 and PeSCL7 were investigated with different RGs. The results, calculated using qBasePlus software, showed that compared with the least‐appropriate RGs, the expression profiles normalized by the recommended RGs were closer to expectations. Our study provided an important RG application guideline for P. euphratica gene expression characterization.
Drought is a critical environmental factor which constrains plant survival and growth. Genetic engineering provides a credible strategy to improve drought tolerance of plants. Here, we generated ...transgenic poplar lines expressing the isopentenyl transferase gene (IPT) under the driver of PtRD26 promoter (PtRD26pro‐IPT). PtRD26 is a senescence and drought‐inducible NAC transcription factor. PtRD26pro‐IPT plants displayed multiple phenotypes, including improved growth and drought tolerance. Transcriptome analysis revealed that auxin biosynthesis pathway was activated in the PtRD26pro‐IPT plants, leading to an increase in auxin contents. Biochemical analysis revealed that ARABIDOPSIS RESPONSE REGULATOR10 (PtARR10), one of the type‐B ARR transcription factors in the cytokinin pathway, was induced in PtRD26pro‐IPT plants and directly regulated the transcripts of YUCCA4 (PtYUC4) and YUCCA5 (PtYUC5), two enzymes in the auxin biosynthesis pathway. Overexpression of PtYUC4 enhanced drought tolerance, while simultaneous silencing of PtYUC4/5 evidently attenuated the drought tolerance of PtRD26pro‐IPT plants. Intriguingly, PtYUC4/5 displayed a conserved thioredoxin reductase activity that is required for drought tolerance by deterring reactive oxygen species accumulation. Our work reveals the molecular basis of cytokinin and auxin interactions in response to environmental stresses, and shed light on the improvement of drought tolerance without a growth penalty in trees by molecular breeding.
Transgenic poplar plants expressing the cytokinin biosynthesis enzyme isopentenyl transferase under the control of a senescence‐ and drought‐inducible promoter display improved growth and drought‐tolerance phenotypes via effects on auxin biosynthesis and detoxification of reactive oxygen species.
Summary
MicroRNAs are essential in plant development and stress resistance, but their specific roles in drought stress require further investigation.
Here, we have uncovered that a Populus‐specific ...microRNAs (miRNA), miR6445, targeting NAC (NAM, ATAF, and CUC) family genes, is involved in regulating drought tolerance of poplar.
The expression level of miR6445 was significantly upregulated under drought stress; concomitantly, seven targeted NAC genes showed significant downregulation. Silencing the expression of miR6445 by short tandem target mimic technology significantly decreased the drought tolerance in poplar. Furthermore, 5′ RACE experiments confirmed that miR6445 directly targeted NAC029. The overexpression lines of PtrNAC029 (OE‐NAC029) showed increased sensitivity to drought compared with knockout lines (Crispr‐NAC029), consistent with the drought‐sensitive phenotype observed in miR6445‐silenced strains. PtrNAC029 was further verified to directly bind to the promoters of glutathione S‐transferase U23 (GSTU23) and inhibit its expression. Both Crispr‐NAC029 and PtrGSTU23 overexpressing plants showed higher levels of PtrGSTU23 transcript and GST activity while accumulating less reactive oxygen species (ROS). Moreover, poplars overexpressing GSTU23 demonstrated enhanced drought tolerance.
Taken together, our research reveals the crucial role of the miR6445‐NAC029‐GSTU23 module in enhancing poplar drought tolerance by regulating ROS homeostasis. This finding provides new molecular targets for improving the drought resistance of trees.
Leaf senescence is an essential physiological process that is accompanied by the remobilization of nutrients from senescent leaves to young leaves or other developing organs. Although leaf senescence ...is a genetically programmed process, it can be induced by a wide variety of biotic and abiotic factors. Accumulating studies demonstrate that senescence-associated transcription factors (Sen-TFs) play key regulatory roles in controlling the initiation and progression of leaf senescence process. Interestingly, recent functional studies also reveal that a number of Sen-TFs function as positive or negative regulators of plant immunity. Moreover, the plant hormone salicylic acid (SA) and reactive oxygen species (ROS) have been demonstrated to be key signaling molecules in regulating leaf senescence and plant immunity, suggesting that these two processes share similar or common regulatory networks. However, the interactions between leaf senescence and plant immunity did not attract sufficient attention to plant scientists. Here, we review the regulatory roles of SA and ROS in biotic and abiotic stresses, as well as the cross-talks between SA/ROS and other hormones in leaf senescence and plant immunity, summarize the transcriptional controls of Sen-TFs on SA and ROS signal pathways, and analyze the cross-regulation between senescence and immunity through a broad literature survey. In-depth understandings of the cross-regulatory mechanisms between leaf senescence and plant immunity will facilitate the cultivation of high-yield and disease-resistant crops through a molecular breeding strategy.
Gibberellic acid-stimulated
(GASA) proteins, as cysteine-rich peptides (CRPs), play roles in development and reproduction and biotic and abiotic stresses. Although the
gene family has been identified ...in plants, the knowledge about GASAs in
, the woody model plant for studying abiotic stress, remains limited. Here, we referenced the well-sequenced
genome, and identified the GASAs in the whole genome of
and
. 21 candidate genes in
and 19 candidate genes in
were identified and categorized into three subfamilies by phylogenetic analysis. Most GASAs with signal peptides were located extracellularly. The
genes in
have experienced multiple gene duplication events, especially in the subfamily A. The evolution of the subfamily A, with the largest number of members, can be attributed to whole-genome duplication (WGD) and tandem duplication (TD). Collinearity analysis showed that WGD genes played a leading role in the evolution of
genes subfamily B. The expression patterns of
and
were investigated using the PlantGenIE database and the real-time quantitative PCR (qRT-PCR), respectively.
genes in
and
were mainly expressed in young tissues and organs, and almost rarely expressed in mature leaves.
genes in
leaves were also widely involved in hormone responses and drought stress responses. GUS activity assay showed that PeuGASA15 was widely present in various organs of the plant, especially in vascular bundles, and was induced by auxin and inhibited by mannitol dramatically. In summary, this present study provides a theoretical foundation for further research on the function of
genes in
.
Summary
In the present study, PeSTZ1, a cysteine‐2/histidine‐2‐type zinc finger transcription factor, was isolated from the desert poplar, Populus euphratica, which serves as a model stress ...adaptation system for trees. PeSTZ1 was preferentially expressed in the young stems and was significantly up‐regulated during chilling and freezing treatments. PeSTZ1 was localized to the nucleus and bound specifically to the PeAPX2 promoter. To examine the potential functions of PeSTZ1, we overexpressed it in poplar 84K hybrids (Populus alba × Populus glandulosa), which are known to be stress‐sensitive. Upon exposure to freezing stress, transgenic poplars maintained higher photosynthetic activity and dissipated more excess light energy (in the form of heat) than wild‐type poplars. Thus, PeSTZ1 functions as a transcription activator to enhance freezing tolerance without sacrificing growth. Under freezing stress, PeSTZ1 acts upstream of ASCORBATE PEROXIDASE2 (PeAPX2) and directly regulates its expression by binding to its promoter. Activated PeAPX2 promotes cytosolic APX that scavenges reactive oxygen species (ROS) under cold stress. PeSTZ1 may operate in parallel with C‐REPEAT‐BINDING FACTORS to regulate COLD‐REGULATED gene expression. Moreover, PeSTZ1 up‐regulation reduces malondialdehyde and ROS accumulation by activating the antioxidant system. Taken together, these results suggested that overexpressing PeSTZ1 in 84K poplar enhances freezing tolerance through the modulation of ROS scavenging via the direct regulation of PeAPX2 expression.
PDF
