Abscisic acid collaborates with lignin and flavonoid to improve pre-silking drought tolerance by tuning stem elongation and ear development in maize (Zea mays L.)

Drought stress memory in maize: understanding and harnessing the past for future resilience

Maize (Zea mays L.), a cornerstone of global food security, faces significant challenges due to drought stress, which disrupts its growth, development, and productivity. This review synthesizes advances in our understanding of drought stress memory, a mechanism that enables maize to "remember" prior drought exposure through transcriptional, epigenetic, and physiological pathways. Key regulators, including transcription factors (ZmEREB24 and ZmNF-YC12) and epigenetic modifications (DNA methylation and histone acetylation), orchestrate stress-responsive pathways that ensure rapid adaptation to recurrent drought events. Complementing these molecular mechanisms, physiological adaptations, such as optimized root and leaf architecture, enhanced water-use efficiency, and antioxidant defenses, further strengthen drought tolerance. Practical applications, including molecular priming techniques (e.g., osmopriming, hydropriming, nanoparticles) and advanced genetic tools (CRISPR/Cas9, GWAS), promise scalable solutions for breeding drought-resilient maize varieties. Despite this progress, challenges remain, including genotype-specific variability, scalability, and trade-offs between resilience and yield. This review provides a roadmap for integrating laboratory discoveries with field-level practices, bridging molecular and agronomic innovations to address climate variability and ensure sustainable maize production and global food security.

Siblicide between fertilized and unfertilized ovaries within the maize ear

Evolutionarily, plants overproduce ovaries but selectively eliminate those inferiors to ensure competitive offspring to set. This sibling rivalry, reducing grain number, is detrimental agronomically. However, the interaction between early-fertilized and unfertilized ovaries in sequentially-pollinated panicles is unclear. Here, we fertilized the ovaries on half rows of maize ear (HP) while keeping the rest unfertilized to investigate their interaction. HP reduced the growth of unfertilized ovaries while promoting fertilized ovary (grain) development. 13C-isotope labeling of grains led to isotope signal detected in the unlabeled ovaries, validating their interactions. Transcriptionally, HP caused cell wall degradation and senescence of unfertilized ovaries, reducing their viability. These ovaries showed promoted auxin and jasmonic acid levels with activated auxin signaling but suppressed MAPK signaling. Conversely, HP grains activated MAPK signaling, sugar utilization, and cell proliferation. These findings demonstrate that grains suppress ovaries in ear to consolidate sugar utilization advantage for development, potentially through hormone and MAPK signaling.

Combined transcriptional and metabolomic analysis of flavonoids in the regulation of female flower bud differentiation in Juglans sigillata Dode

Juglans sigillata Dode is rich in flavonoids, but the low ratio of female to male flower buds limits the development of the J. sigillata industry. While the abundance of flavonoids in J. sigillata is known, whether flavonoids influence female flower bud differentiation has not been reported. In this study, we explored the regulatory mechanisms of gene expression and metabolite accumulation during female flower bud differentiation through integrated transcriptomic and metabolomic analyses. Our findings revealed that flavonoid biosynthesis is a key pathway influencing female flower bud differentiation, with metabolites primarily shifting towards the isoflavonoid, flavone, and flavonol branches. Structural genes such as chalcone synthase, dihydroflavonol 4-reductase, flavonol synthase, and flavonoid 3',5'-hydroxylase were identified as playing crucial regulatory roles. The expression of these genes promoted the accumulation of flavonoids, which in turn influenced female flower bud differentiation by modulating key regulatory genes including Suppressor of Overexpression of Constans1, Constans, Flowering Locus T, and APETALA1. Furthermore, transcription factors (TFs) highly expressed during the physiological differentiation of female flower buds, particularly M-type MADS, WRKY, and MYB, were positively correlated with flavonoid biosynthesis genes, indicating their significant role in the regulation of flavonoid production. These results offer valuable insights into the mechanisms of female flower bud differentiation in J. sigillata and highlight the regulatory role of flavonoids in plant bud differentiation.

The Class III Peroxidase gene TaPRX-2A controls grain number per spike in common wheat (Triticum aestivum L.)

Some peroxidases (PRXs) are involved in abiotic stress response. However, to the best of our knowledge, the effects of PRXs on agronomic traits including grain number per spike (GNS), spikelet number per spike (SNS) and spike length (SL) are also largely unknown. In our study, we cloned a wheat PRX gene TaPRX-2A and identified its function in controlling GNS by generating transgenic overexpression lines. The results showed that TaPRX-2A overexpression displayed lower GNS and shorter SL, compared with the wild-type plants. RNA-seq analysis indicated alterations in various pathways including flavonoid biosynthesis, lignin biosynthesis, phytohormone signaling, as well as sucrose and starch biosynthesis. Co-expression analysis showed that transcription factors, such as bHLH, WRKY, and bZIP may be involved in the regulation of various genes associated with these pathways. Our findings provide insights into the mechanisms by which PRXs regulate agronomic traits, illustrating potential applicability in crop improvement programs.

Integrated transcriptomic and metabolomic analyses reveal that MsSPHK1 - A sphingosine kinase gene negatively regulates drought tolerance in alfalfa (Medicago sativa L.)

Alfalfa is a valuable forage crop but voluntarily affected by drought. Understanding the mechanisms of drought resistance in alfalfa is crucial for improving resilient cultivars. In our study, we used four distinct alfalfa accessions two drought-tolerance (DT) and two drought-sensitive (DS) and identified transcriptional modules and candidate genes associated with the drought tolerance in the DS from transcriptomic analyses. Our metabolic profiling of 520 metabolites revealed significant variations between the DS and DT groups, particularly in the levels of flavonoids and nucleotides and their derivatives. The integrated analysis of transcriptome and metabolome analysis revealed that the glycine, serine, and threonine metabolism and the sphingolipid metabolism are associated with the drought resistance. When drought stress occurs, MsSRR (MsG 0180002649.01) and MsSPHK1 (MsG 0280006618.01) are significantly up-regulated, L-serine and dihydrosphingosine (DHS) significantly down-regulated in DS. By silencing the MsSPHK1 gene we found the drought resistance was significantly improved. This was evidenced by a significant increase in the activity of antioxidant enzymes such as SOD, POD, and CAT, compared to the control group. Additionally, the photosynthetic rate, stomatal conductance, and efficiency of photosystem II measured by Fv/Fm, phi2 and qL, were significantly higher in the silenced plants than in the control group. In conclusion, our results suggest that the increased level of dihydrosphingosine improves alfalfa resistance to drought stress. Moreover, the negative regulatory role of MsSPHK1 in drought tolerance provides a promising target for genetic manipulation to enhance the resilience of alfalfa to drought stress.

The MdIAA29-MdARF4 complex plays an important role in balancing plant height with salt and drought stress responses

Breeding dwarf apple (Malus domestica) varieties is a recent trend in agriculture because such varieties are easy to maintain and have high yields; however, dwarf apple trees generally have poor stress tolerance. Balancing apple plant height and stress response has been an important breeding goal. In this study, aux/indole-3-acetic acid 29 gene in apple (MdIAA29) overexpression lines (#1, #2, and #3) had reduced plant height by 39%, 31%, and 35%, respectively, suitable for close planting applications. Surprisingly, the dwarf MdIAA29-overexpressing lines also showed increased plant tolerance to salt and drought stresses. Further analysis showed that MdIAA29 inhibited the regulation of auxin response factor 4 (ARF4) on Gretchen Hagen 3.9 (GH3.9) gene and 9-cis-epoxycarotenoid dioxygenase 3 (NCED3) gene in apple and changed the contents of auxin and abscisic acid in different tissues, thus achieving a balance between plant height and stress tolerance. In addition, we also found that MdIAA7 enhanced the inhibitory effect of MdIAA29 on MdARF4. In brief, the MdIAA29-MdARF4 complex significantly impacts the height of apple plants and their ability to respond to salt and drought stress.

Transcriptional Profiling Analysis Providing Insights into the Harsh Environments Tolerance Mechanisms of Krascheninnikovia arborescens

Krascheninnikovia arborescens, an endemic shrub in China, thrives in desertification-prone environments due to its robust biomass, hairy leaves, and extensive root system. It is vital for ecological restoration and serves as a valuable forage plant. This study explored the molecular mechanisms underlying K. arborescens' adaptation to desert conditions, focusing on its physiological, biochemical, and transcriptomic responses to drought, salt, and alkali stresses. The results revealed that the three stresses have significant impacts on the photosynthetic, antioxidant, and ion balance systems of the plants, with the alkali stress inducing the most pronounced changes and differential gene expression. The clustering and functional enrichment analyses of differentially expressed genes (DEGs) highlighted the enrichment of the induced genes in pathways related to plant hormone signaling, phenylpropanoid biosynthesis, and transcription factors following stress treatments. In these pathways, the synthesis and signal transduction of abscisic acid (ABA) and ethylene, as well as the flavonoid and lignin synthesis pathways, and transcription factors such as MYB, AP2/ERF, bHLH, NAC, and WRKY responded actively to the stress and played pivotal roles. Through the WGCNA analysis, 10 key modules were identified, with the yellow module demonstrating a high correlation with the ABA and anthocyanin contents, while the turquoise module was enriched in the majority of genes related to hormone and phenylpropanoid pathways. The analysis of hub genes in these modules highlighted the significant roles of the bHLH and MYB transcription factors. These findings could offer new insights into the molecular mechanisms that enable the adaptation of K. arborescens to desert environments, enhancing our understanding of how other desert plants adapt to harsh conditions. These insights are crucial for exploring and utilizing high-quality forage plant germplasm resources and ecological development, with the identified candidate genes serving as valuable targets for further research on stress-resistant genes.

Incomplete filling in the basal region of maize endosperm: timing of development of starch synthesis and cell vitality

Starch synthesis in maize endosperm adheres to the basipetal sequence from the apex downwards. However, the mechanism underlying nonuniformity among regions of the endosperm in starch accumulation and its significance is poorly understood. Here, we examined the spatiotemporal transcriptomes and starch accumulation dynamics in apical (AE), middle (ME), and basal (BE) regions of endosperm throughout the filling stage. Results demonstrated that the BE had lower levels of gene transcripts and enzymes facilitating starch synthesis, corresponding to incomplete starch storage at maturity, compared with AE and ME. Contrarily, the BE showed abundant gene expression for genetic processing and slow progress in physiological development (quantified by an index calculated from the expression values of development progress marker genes), revealing a sustained cell vitality of the BE. Further analysis demonstrated a significant parabolic correlation between starch synthesis and physiological development. An in-depth examination showed that the BE had more active signaling pathways of IAA and ABA than the AE throughout the filling stage, while ethylene showed the opposite pattern. Besides, SNF1-related protein kinase1 (SnRK1) activity, a regulator for starch synthesis modulated by trehalose-6-phosphate (T6P) signaling, was kept at a lower level in the BE than the AE and ME, corresponding to the distinct gene expression in the T6P pathway in starch synthesis regulation. Collectively, the findings support an improved understanding of the timing of starch synthesis and cell vitality in regions of the endosperm during development, and potential regulation from hormone signaling and T6P/SnRK1 signaling.

Streptomyces improves sugarcane drought tolerance by enhancing phenylalanine biosynthesis and optimizing the rhizosphere environment

Drought stress is a common hazard faced by sugarcane growth, and utilizing microorganisms to enhance plant tolerance to abiotic stress has become an important method for sustainable agricultural development. Several studies have demonstrated that Streptomyces chartreuses WZS021 improves sugarcane tolerance to drought stress. However, the molecular mechanisms underlying tolerance at the transcriptional and metabolomic levels remain unclear. We comprehensively evaluated the physiological and molecular mechanisms by which WZS021 enhances drought tolerance in sugarcane, by performing transcriptome sequencing and non-targeted metabolomics; and examining rhizosphere soil properties and plant tissue antioxidant capacity. WZS021 inoculation improved the rhizosphere nutritional environment (AP, ammonia, OM) of sugarcane and enhanced the antioxidant capacity of plant roots, stems, and leaves (POD, SOD, CAT). Comprehensive analyses of the transcriptome and metabolome revealed that WZS021 mainly affects plant drought tolerance through phenylalanine metabolism, plant hormone signal transduction, and flavonoid biosynthesis pathways. The drought tolerance signaling molecules mediated by WZS021 include petunidin, salicylic acid, α-Linoleic acid, auxin, geranylgeraniol and phenylalanine, as well as key genes related to plant hormone signaling transduction (YUCCA, amiE, AUX, CYPs, PAL, etc.). Interestingly, inoculation with WZS021 during regular watering induces a transcriptome-level response to biological stress in sugarcane plants. This study further elucidates a WZS021-dependent rhizosphere-mediated regulatory mechanism for improving sugarcane drought tolerance, providing a theoretical basis for increasing sugarcane production capacity.

A Novel MsEOBI-MsPAL1 Module Enhances Salinity Stress Tolerance, Floral Scent Emission and Seed Yield in Alfalfa

Alfalfa (Medicago sativa L.) is an important and widely cultivated forage legume, yet its yield is constrained by salinity stress. In this study, we characterized an R2R3-MYB transcription factor MsEOBI in alfalfa. Its salt tolerance function and regulatory pathways were investigated. The nuclear-localized MsEOBI functions as a transcriptional activator, enhancing salinity tolerance by promoting the biosynthesis of flavonoids and lignin, as well as facilitating the scavenging of reactive oxygen species (ROS). Additionally, MsEOBI promotes pollinator attraction and increases seed yield by activating the biosynthesis of volatile phenylpropanoids. Yeast one-hybrid (Y1H), dual-luciferase reporter and chromatin immunoprecipitation coupled with quantitative PCR (ChIP-qPCR) assays demonstrated that MsEOBI directly binds to the promoter regions of MsPAL1, a key gene in the phenylpropanoid pathway, thereby activating its expression. Overexpression of MsPAL1 enhances salinity tolerance in alfalfa. These findings elucidate the role of the MsEOBI-MsPAL1 regulatory module and provide valuable genetic resources for the future breeding of salt-tolerant alfalfa varieties.

Genetic, molecular and physiological crosstalk during drought tolerance in maize (Zea mays): pathways to resilient agriculture

MAIN CONCLUSION

This review comprehensively elucidates maize drought tolerance mechanisms, vital for global food security. It highlights genetic networks, key genes, CRISPR-Cas applications, and physiological responses, guiding resilient variety development. Maize, a globally significant crop, confronts the pervasive challenge of drought stress, impacting its growth and yield significantly. Drought, an important abiotic stress, triggers a spectrum of alterations encompassing maize's morphological, biochemical, and physiological dimensions. Unraveling and understanding these mechanisms assumes paramount importance for ensuring global food security. Approaches like developing drought-tolerant varieties and harnessing genomic and molecular applications emerge as effective measures to mitigate the negative effects of drought. The multifaceted nature of drought tolerance in maize has been unfolded through complex genetic networks. Additionally, quantitative trait loci mapping and genome-wide association studies pinpoint key genes associated with drought tolerance, influencing morphophysiological traits and yield. Furthermore, transcription factors like ZmHsf28, ZmNAC20, and ZmNF-YA1 play pivotal roles in drought response through hormone signaling, stomatal regulation, and gene expression. Genes, such as ZmSAG39, ZmRAFS, and ZmBSK1, have been reported to be pivotal in enhancing drought tolerance through diverse mechanisms. Integration of CRISPR-Cas9 technology, targeting genes like gl2 and ZmHDT103, emerges as crucial for precise genetic enhancement, highlighting its role in safeguarding global food security amid pervasive drought challenges. Thus, decoding the genetic and molecular underpinnings of drought tolerance in maize sheds light on its resilience and paves the way for cultivating robust and climate-smart varieties, thus safeguarding global food security amid climate challenges. This comprehensive review covers quantitative trait loci mapping, genome-wide association studies, key genes and functions, CRISPR-Cas applications, transcription factors, physiological responses, signaling pathways, offering a nuanced understanding of intricate mechanisms involved in maize drought tolerance.

Deciphering the maize gene ZmGF14-3: implications for plant height based on co-expression networks

The evolutionary analysis showed that the GF14 family was conserved, however, there was limited evidence linking GF14s to plant height. In our investigations, we discovered a co-expression relationship between ZmGF14s and functionally characterized genes linked to plant height. In the co-expression network, we identified ZmGF14-3, a gene expression exhibiting a positive correlation with plant height in three maize varieties, we postulated that this gene could be intimately linked to plant height development. Subsequently, we cloned ZmGF14-3 from the maize B73 inbred line and overexpressed it in Arabidopsis, resulting in markedly dwarfed transgenic phenotypes. Measurements of endogenous phytohormones disclosed a significant reduction in concentrations of Gibberellic Acid 7 (GA7) and Indole-3-Acetic Acid (IAA) in the overexpressed Arabidopsis, furthermore, qPCR results highlighted a pronounced decrease in the expression levels of plant height-related genes when compared to the wild type, therefore, it is plausible to posit that ZmGF14-3 plays a pivotal role in regulating the growth and development of maize through interactions with various phytohormone-related genes. Thus, delving into the potential interactions between ZmGF14-3 and these genes holds the promise of yielding valuable insights into the molecular mechanisms underpinning plant height development in maize.

Molecular mechanisms underlying low temperature inhibition of grain filling in maize (Zea mays L.): coordination of growth and cold responses

Low temperature (LT) greatly restricts grain filling in maize (Zea mays L.), but the relevant molecular mechanisms are not fully understood. To better understand the effect of LT on grain development, 17 hybrids were subjected to LT stress in field trials over 3 years, and two hybrids of them with contrasting LT responses were exposed to 30/20°C and 20/10°C for 7 days during grain filling in a greenhouse. At LT, thousand-kernel weight declined, especially in LT-sensitive hybrid FM985, while grain-filling rate was on average about 48% higher in LT-tolerant hybrid DK159 than FM985. LT reduced starch synthesis in kernel mainly by suppression of transcript levels and enzyme activities for sucrose synthase and hexokinase. Brassinolide (BR) was abundant in DK159 kernel, and genes involved in BR and cytokinin signals were inducible by stress. LT downregulated the genes in light-harvesting complex and photosystem I/II subunits, accompanied by reduced photosynthetic rate and Fv/Fm in ear leaf. The LT-tolerant hybrid could maintain a high soluble sugar content and fast interconversion between sucrose and hexose in the stem internode and cob, improving assimilate allocation to kernel at LT stress and paving the way for simultaneous growth and LT stress responses.

Differential Transcription Profiling Reveals the MicroRNAs Involved in Alleviating Damage to Photosynthesis under Drought Stress during the Grain Filling Stage in Wheat

To explore the possible novel microRNA (miRNA) regulatory pathways in Zhengmai 1860, a newly cultivated drought-tolerant wheat (Triticum aestivum L.) cultivar, miRNA transcriptome sequencing of the flag leaves of Zhengmai 1860, drought-sensitive variety Zhoumai 18, and drought-resistant variety Bainong 207 was performed during the grain filling stage. We also observed changes in the chloroplast ultrastructure, phytohormone levels, and antioxidant- and photosynthesis-related physiological indicators in three wheat varieties. The results showed that the flag leaves of the drought-tolerant variety Zhengmai 1860 had higher chlorophyll contents and net photosynthetic rates than those of Zhoumai 18 under drought stress during the grain filling stage; in addition, the chloroplast structure was more complete. However, there was no significant difference between Zhengmai 1860 and Bainong 207. MiRNA transcriptome analysis revealed that the differential expression of the miRNAs and mRNAs exhibited variable specificity. The KEGG pathway enrichment results indicated that most of the genes were enriched in the MAPK signaling pathway, plant hormone signal transduction, photosynthetic antennae protein, and amino acid and carbohydrate metabolism. In the drought-tolerant cultivar Zhengmai 1860, tae-miR408 was targeted to regulate the allene oxide synthase (AOS) gene, inhibit its expression, reduce the AOS content, and decrease the synthesis of jasmonic acid (JA) and abscisic acid (ABA). The results of this study suggest that Zhengmai 1860 could improve the photosynthetic performance of flag leaves by inhibiting the expression of genes involved in the JA pathway through miRNAs under drought conditions. Moreover, multiple miRNAs may target chlorophyll, antioxidant enzymes, phytohormone signal transduction, and other related pathways; thus, it is possible to provide a more theoretical basis for wheat molecular breeding.

Identification of a novel marker and its associated laccase gene for regulating ear length in tropical and subtropical maize lines

KEY MESSAGE

This study revealed the identification of a novel gene, Zm00001d042906, that regulates maize ear length by modulating lignin synthesis and reported a molecular marker for selecting maize lines with elongated ears. Maize ear length has garnered considerable attention due to its high correlation with yield. In this study, six maize inbred lines of significant importance in maize breeding were used as parents. The temperate maize inbred line Ye107, characterized by a short ear, was crossed with five tropical or subtropical inbred lines featuring longer ears, creating a multi-parent population displaying significant variations in ear length. Through genome-wide association studies and mutation analysis, the A/G variation at SNP_183573532 on chromosome 3 was identified as an effective site for discriminating long-ear maize. Furthermore, the associated gene Zm00001d042906 was found to correlate with maize ear length. Zm00001d042906 was functionally annotated as a laccase (Lac4), which showed activity and influenced lignin synthesis in the midsection cells of the cob, thereby regulating maize ear length. This study further reports a novel molecular marker and a new gene that can assist maize breeding programs in selecting varieties with elongated ears.

Polyamines mediate the inhibitory effect of drought stress on nitrogen reallocation and utilization to regulate grain number in wheat

Drought stress poses a serious threat to grain formation in wheat. Nitrogen (N) plays crucial roles in plant organ development; however, the physiological mechanisms by which drought stress affects plant N availability and mediates the formation of grains in spikes of winter wheat are still unclear. In this study, we determined that pre-reproductive drought stress significantly reduced the number of fertile florets and the number of grains formed. Transcriptome analysis demonstrated that this was related to N metabolism, and in particular, the metabolism pathways of arginine (the main precursor for synthesis of polyamine) and proline. Continuous drought stress restricted plant N accumulation and reallocation rates, and plants preferentially allocated more N to spike development. As the activities of amino acid biosynthesis enzymes and catabolic enzymes were inhibited, more free amino acids accumulated in young spikes. The expression of polyamine synthase genes was down-regulated under drought stress, whilst expression of genes encoding catabolic enzymes was enhanced, resulting in reductions in endogenous spermidine and putrescine. Treatment with exogenous spermidine optimized N allocation in young spikes and leaves, which greatly alleviated the drought-induced reduction in the number of grains per spike. Overall, our results show that pre-reproductive drought stress affects wheat grain numbers by regulating N redistribution and polyamine metabolism.

FlbZIP12 gene enhances drought tolerance via modulating flavonoid biosynthesis in Fagopyrum leptopodum

Karst lands provide a poor substrate to support plant growth, as they are low in nutrients and water content. Common buckwheat (Fagopyrum esculentum) is becoming a popular crop for its gluten-free grains and their high levels of phenolic compounds, but buckwheat yields are affected by high water requirements during grain filling. Here, we describe a wild population of drought-tolerant Fagopyrum leptopodum and its potential for enhancing drought tolerance in cultivated buckwheat. We determined that the expression of a gene encoding a Basic leucine zipper (bZIP) transcription factor, FlbZIP12, from F. leptopodum is induced by abiotic stresses, including treatment with the phytohormone abscisic acid, salt, and polyethylene glycol. In addition, we show that overexpressing FlbZIP12 in Tartary buckwheat (Fagopyrum tataricum) root hairs promoted drought tolerance by increasing the activities of the enzymes superoxide dismutase and catalase, decreasing malondialdehyde content, and upregulating the expression of stress-related genes. Notably, FlbZIP12 overexpression induced the expression of key genes involved in flavonoid biosynthesis. We also determined that FlbZIP12 interacts with protein kinases from the FlSnRK2 family in vitro and in vivo. Taken together, our results provide a theoretical basis for improving drought tolerance in buckwheat via modulating the expression of FlbZIP12 and flavonoid contents.

Systematic Identification and Functional Analysis of the Hypericum perforatum L. bZIP Gene Family Indicating That Overexpressed HpbZIP69 Enhances Drought Resistance

Basic leucine zipper (bZIP) transcription factors play significant roles in plants' growth and development processes, as well as in response to biological and abiotic stresses. Hypericum perforatum is one of the world's top three best-selling herbal medicines, mainly used to treat depression. However, there has been no systematic identification or functional analysis of the bZIP gene family in H. perforatum. In this study, 79 HpbZIP genes were identified. Based on phylogenetic analysis, the HpbZIP gene family was divided into ten groups, designated A-I and S. The physicochemical properties, gene structures, protein conserved motifs, and Gene Ontology enrichments of all HpbZIPs were systematically analyzed. The expression patterns of all genes in different tissues of H. perforatum (i.e., root, stem, leaf, and flower) were analyzed by qRT-PCR, revealing the different expression patterns of HpbZIP under abiotic stresses. The HpbZIP69 protein is localized in the nucleus. According to the results of the yeast one-hybrid (Y1H) assays, HpbZIP69 can bind to the HpASMT2 (N-acetylserotonin O-methyltransferase) gene promoter (G-box cis-element) to activate its activity. Overexpressing HpbZIP69 in Arabidopsis wild-type lines enhanced their tolerance to drought. The MDA and H2O2 contents were significantly decreased, and the activity of superoxide dismutase (SOD) was considerably increased under the drought stress. These results may aid in additional functional studies of HpbZIP transcription factors, and in cultivating drought-resistant medicinal plants.

Coordination of carbon assimilation, allocation, and utilization for systemic improvement of cereal yield

The growth of yield outputs is dwindling after the first green revolution, which cannot meet the demand for the projected population increase by the mid-century, especially with the constant threat from extreme climates. Cereal yield requires carbon (C) assimilation in the source for subsequent allocation and utilization in the sink. However, whether the source or sink limits yield improvement, a crucial question for strategic orientation in future breeding and cultivation, is still under debate. To narrow the knowledge gap and capture the progress, we focus on maize, rice, and wheat by briefly reviewing recent advances in yield improvement by modulation of i) leaf photosynthesis; ii) primary C allocation, phloem loading, and unloading; iii) C utilization and grain storage; and iv) systemic sugar signals (e.g., trehalose 6-phosphate). We highlight strategies for optimizing C allocation and utilization to coordinate the source-sink relationships and promote yields. Finally, based on the understanding of these physiological mechanisms, we envisage a future scenery of "smart crop" consisting of flexible coordination of plant C economy, with the goal of yield improvement and resilience in the field population of cereals crops.