New Advances in the Regulation of Leaf Senescence by Classical and Peptide Hormones

MYB47 delays leaf senescence by modulating jasmonate pathway via direct regulation of CYP94B3/CYP94C1 expression in Arabidopsis

Leaf senescence is a complex genetic process intricately regulated by multiple layers of control. Transcription factors, as master regulators of gene expression, play crucial roles in initiating and progressing leaf senescence. Through screening an activation-tagged mutant library, we identified MYB47 as a negative regulator of leaf senescence. Constitutive or inducible overexpression of MYB47 significantly delays leaf senescence, while loss-of-function mutants exhibit accelerated senescence. Transcriptome analysis revealed a marked suppression of jasmonic acid (JA) signaling in MYB47 overexpression lines. Conversely, the myb47 mutants display elevated JA levels and reduced expression of JA catabolic genes, CYP94B3 and CYP94C1. Biochemical evidence demonstrated that MYB47 directly binds to the promoters of CYP94B3 and CYP94C1, upregulating their expression. Consequently, JA contents are significantly reduced in MYB47 overexpression lines. Overexpressing CYP94B3 or CYP94C1 in myb47 mutants alleviates their early senescence phenotype. Furthermore, JA induces MYB47 expression, forming a negative feedback loop (JA-MYB47-CYP94B3/C1-JA) that fine-tunes leaf senescence. Our findings reveal a novel regulatory module involving MYB47 and JA signaling that governs leaf senescence. By stimulating JA catabolism and attenuating JA signaling, MYB47 plays a crucial role in delaying leaf senescence.

Willow oak (Quercus phellos) seedling roots continue respiration and growth during fall and winter in a soil temperature-dependent manner

Many greentree reservoirs (GTRs) and other bottomland hardwood forests have experienced a shift in tree species composition away from desired red oaks (Quercus section Lobatae), like willow oak (Quercus phellos L.), due to flood stress mortality. Trees experience flood stress primarily through their root system, so it is surmised that GTR flooding may be occurring before root systems have reduced their activity entering the winter. Because soils buffer seasonal temperature changes, we hypothesized that root activity would respond to the belowground environment rather than the aboveground environment. To investigate whether cold soil temperatures reduce root growth and respiration in willow oak during winter, soil temperatures for container seedlings were either held at 15 °C or transitioned to 10 or 5 °C in the late fall. Root elongation was measured in seedlings grown in rhizotron pots by analyzing repeated images of roots during the fall-winter transition period. Root respiration, measured at soil temperature levels, was used as an indicator of root energetic expenses. Also, root respiration was measured at 15 and 5 °C to determine Q10 values to test for acclimation to low soil temperature. Root elongation continued in winter, even after stem elongation stopped in soil temperatures ≥5 °C, a condition usually met throughout most of the native range of willow oak. Both root elongation and respiration rates decreased in cooler soil temperatures. However, Q10 values were unaffected by soil temperature treatment. These findings do not support root dormancy or cold acclimation of root respiratory activity but indicate that temperature directly and reversibly affected root respiration rate. Root elongation may have been dependent on photoassimilates produced by green leaves that were retained through much of winter. Overall, our results suggest that willow oak roots may continue a high rate of growth throughout winter, unlike most temperate species measured to date, and that soil temperature has a major influence over their growth and respiration rates.

Genome-wide association study of image-based trait reveals the genetic architecture of dark-induced leaf senescence in rice

Darkness is often used as an effective measure to induce leaf senescence. Although many senescence-related genes in rice have been reported, the genome-wide genetic architecture underlying leaf senescence remains poorly understood. In our study, indica and japonica rice showed contrasting responses to dark-induced leaf senescence (DILS). Genome-wide association studies (GWAS) combined with transcriptomic analyses revealed 57, 97, and 48 loci involved in the regulation of the onset, progression, and ending of DILS, respectively. Haplotype analyses showed that the senescence-related loci differentially accumulated in indica and japonica accessions and functioned additively to regulate DILS. A total of 357 candidate genes were identified that are involved in various senescence-related processes such as lipid and amino acid catabolism, photosynthesis, response to reactive oxygen species, and regulation of defence response. In addition, functional analyses of candidate genes revealed that OsMYB21 positively regulates the onset of DILS, while OsSUB1B negatively regulates its progression. Thus, our results provide new insights into the genetic regulation of DILS in rice.

The RING-type E3 ligase RIE1 sustains leaf longevity by specifically targeting AtACS7 to fine-tune ethylene production in Arabidopsis

Ethylene is widely recognized as a positive regulator of leaf senescence. However, how plants coordinate the biosynthesis of ethylene to meet the requirements of senescence progression has not been determined. The rate-limiting enzyme in the ethylene biosynthesis pathway is ACC synthase. AtACS7 was previously considered one of the major contributors to the synthesis of "senescence ethylene" in Arabidopsis. However, the "brake signal" that fine-tunes the expression of AtACS7 to ensure optimal ethylene production during leaf development has yet to be identified. In the present study, the RING-H2 zinc-finger protein RIE1 was found to specifically interact with and ubiquitinate AtACS7, among all functional ACSs in Arabidopsis, to promote its degradation. Overexpression of RIE1 markedly decreased ethylene biosynthesis and delayed leaf senescence, whereas loss of function of RIE1 significantly increased ethylene emission and accelerated leaf senescence. The ethylene-related phenotypes of RIE1 overexpressing or knockout mutants were effectively rescued by the ethylene precursor ACC or the competitive inhibitor of ACS, respectively. In particular, AtACS7-induced precocious leaf senescence was strongly enhanced by the loss of RIE1 but was significantly attenuated by the overexpression of RIE1. The specific regions of interaction between AtACS7 and RIE1, as well as the major ubiquitination sites of AtACS7, were further investigated. All results demonstrated that RIE1 functions as an important modulator of ethylene biosynthesis during leaf development by specifically targeting AtACS7 for degradation, thereby enabling plants to produce the optimal levels of ethylene needed.

The interplay of growth-regulating factor 5 and BZR1 in coregulating chlorophyll degradation in poplar

Chlorophyll (Chl) is essential for plants to carry out photosynthesis, growth and development processes. Growth-regulating factors (GRFs) play a vital role in regulating Chl degradation in plants. However, the molecular mechanism by which GRF5 regulates Chl degradation in poplar remains unknown. Here we found that overexpression of PpnGRF5-1 increased Chl content in leaves and promoted chloroplast development in poplar. Overexpression of PpnGRF5-1 in poplar delayed Chl degradation induced by external factors, such as hormones, darkness and salt stress. PpnGRF5-1 responded to brassinosteroid (BR) signalling during BR-induced Chl degradation and reduced the expression levels of Chl degradation and senescence-related genes. PpnGRF5-1 inhibited the expression of Chl b reductases PagNYC1 and PagNOL. PpnGRF5-1 could interact with PagBZR1 in the nucleus. PagBZR1 also inhibited the expression of PagNYC1. In addition, we found that the protein-protein interaction between PagBZR1 and PpnGRF5-1 enhanced the inhibitory effect of PpnGRF5-1 on the Chl b reductases PagNYC1 and PagNOL. BZR1 and GRF5-1 were upregulated, and NOL and NYC1 were downregulated in triploid poplars compared to diploids. This study revealed a new mechanism by which PpnGRF5-1 regulates Chl degradation in poplars and lays the foundation for comprehensively analysing the molecular mechanism of Chl metabolism in triploid poplars.

Identification of transcription factors associated with leaf senescence in tobacco

Leaf senescence represents the final stage of leaf development, involving transcription factors (TFs)-mediated genetic reprogramming events. The timing of crop leaf senescence has a major influence on the yield and quality of crop in agricultural production. As important regulator of plant growth, the significance of TFs in the regulation of leaf senescence have been highlighted in various plant species by recent advances in genetics. However, studies on underlying molecular mechanisms are still not adequately explained. In this study, for analyzing the regulation of TFs on senescence of tobacco leaves, we combined gene differential expression analysis with weighted gene co-expression network analysis (WGCNA) to analyze the time-series gene expression profiles in senescing tobacco leaf. Among 3517 TF genes expressed in tobacco leaves, we identified 21, 35, and 183 TFs that were associated with early, middle, and late stages of tobacco leaf senescence, respectively. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation results reveal that these senescence response TFs are correlated with several biological pathways such as plant hormone signal transduction, ubiquitin mediated proteolysis and MAPK signaling pathway, indicating the roles of TFs in regulating leaf senescence. Our results provide implications for future studies of the potential regulatory mechanisms of TFs involved in senescence of tobacco leaves.

OsNAC121 regulates root development, tillering, panicle morphology, and grain filling in rice plant

Transcription factors in coordination with phytohormones form an intricate regulatory network modulating vital cellular mechanisms like development, growth and senescence in plants. In this study, we have functionally characterized the transcription factor OsNAC121 by developing gene silencing and overexpressing transgenic rice plants, followed by detailed analyses of the plant architecture. Transgenic lines exhibited remodelling in crown root development, lateral root structure and density, tiller height and number, panicle and grain morphologies, underpinning the imbalanced auxin: cytokinin ratio due to perturbed auxin transportation. Application of cytokinin, auxin and abscisic acid increased OsNAC121 gene expression nearly 17-, 6- and 91-folds, respectively. qRT-PCR results showed differential expressions of auxin and cytokinin pathway genes, implying their altered levels. A 47-fold higher expression level of OsNAC121 during milky stage in untransformed rice, compared to 14-day old shoot tissue, suggests its crucial role in grain filling; as evidenced by a large number of undeveloped grains produced by the gene silenced lines. Crippled gravitropic response by the transgenic plants indicates their impaired auxin transport. Bioinformatics revealed that OsNAC121 interacts with co-repressor (TOPLESS) proteins and forms a part of the inhibitor complex OsIAA10, an essential core component of auxin signalling pathway. Therefore, OsNAC121 emerges as an important regulator of various aspects of plant architecture through modulation of crosstalk between auxin and cytokinin, altering their concentration gradient in the meristematic zones, and consequently modifying different plant organogenesis processes.

Regulatory Mechanism through Which Old Soybean Leaves Respond to Mn Toxicity Stress

Manganese (Mn) is a heavy metal that can cause excessive Mn poisoning in plants, disrupting microstructural homeostasis and impairing growth and development. However, the specific response mechanisms of leaves to Mn poisoning have not been fully elucidated. This study revealed that Mn poisoning of soybean plants resulted in yellowing of old leaves. Physiological assessments of these old leaves revealed significant increases in the antioxidant enzymes activities (peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT)) and elevated levels of malondialdehyde (MDA), proline, indoleacetic acid (IAA), and salicylic acid (SA), under 100 μM Mn toxicity. Conversely, the levels of abscisic acid (ABA), gibberellin 3 (GA3), and jasmonic acid (JA) significantly decreased. The Mn content in the affected leaves significantly increased, while the levels of Ca, Na, K, and Cu decreased. Transcriptome analysis revealed 2258 differentially expressed genes in the Mn-stressed leaves, 744 of which were upregulated and 1514 were downregulated; these genes included genes associated with ion transporters, hormone synthesis, and various enzymes. Quantitative RT-PCR (qRT-PCR) verification of fifteen genes confirmed altered gene expression in the Mn-stressed leaves. These findings suggest a complex gene regulatory mechanism under Mn toxicity and stress, providing a foundation for further exploration of Mn tolerance-related gene regulatory mechanisms in soybean leaves. Using the methods described above, this study will investigate the molecular mechanism of old soybean leaves' response to Mn poisoning, identify key genes that play regulatory roles in Mn toxicity stress, and lay the groundwork for cultivating high-quality soybean varieties with Mn toxicity tolerance traits.

CLAVATA signaling in plant-environment interactions

Plants must rapidly and dynamically adapt to changes in their environment. Upon sensing environmental signals, plants convert them into cellular signals, which elicit physiological or developmental changes that allow them to respond to various abiotic and biotic cues. Because plants can be simultaneously exposed to multiple environmental cues, signal integration between plant cells, tissues, and organs is necessary to induce specific responses. Recently, CLAVATA3/EMBRYO SURROUNDING REGION-related (CLE) peptides and their cognate CLAVATA-type receptors received increased attention for their roles in plant-environment interactions. CLE peptides are mobile signaling molecules, many of which are induced by a variety of biotic and abiotic stimuli. Secreted CLE peptides are perceived by receptor complexes on the surface of their target cells, which often include the leucine-rich repeat receptor-like kinase CLAVATA1. Receptor activation then results in cell-type and/or environment-specific responses. This review summarizes our current understanding of the diverse roles of environment-regulated CLE peptides in modulating plant responses to environmental cues. We highlight how CLE signals regulate plant physiology by fine-tuning plant-microbe interactions, nutrient homeostasis, and carbon allocation. Finally, we describe the role of CLAVATA receptors in the perception of environment-induced CLE signals and discuss how diverse CLE-CLAVATA signaling modules may integrate environmental signals with plant physiology and development.

Rice Basic Helix-Loop-Helix 079 (OsbHLH079) Delays Leaf Senescence by Attenuating ABA Signaling

Leaf senescence represents the final phase of leaf development and is characterized by a highly organized degenerative process involving the active translocation of nutrients from senescing leaves to growing tissues or storage organs. To date, a large number of senescence-associated transcription factors (sen-TFs) have been identified that regulate the initiation and progression of leaf senescence. Many of these TFs, including NAC (NAM/ATAF1/2/CUC2), WRKY, and MYB TFs, have been implicated in modulating the expression of downstream senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs) under the control of phytohormones. However, the involvement of basic helix-loop-helix (bHLH) TFs in leaf senescence has been less investigated. Here, we show that OsbHLH079 delays both natural senescence and dark-induced senescence: Overexpression of OsbHLH079 led to a stay-green phenotype, whereas osbhlh079 knockout mutation displayed accelerated leaf senescence. Similar to other sen-TFs, OsbHLH079 showed a gradual escalation in expression as leaves underwent senescence. During this process, the mRNA levels of SAGs and CDGs remained relatively low in OsbHLH079 overexpressors, but increased sharply in osbhlh079 mutants, suggesting that OsbHLH079 negatively regulates the transcription of SAGs and CDGs under senescence conditions. Additionally, we found that OsbHLH079 delays ABA-induced senescence. Subsequent RT-qPCR and dual-luciferase reporter assays revealed that OsbHLH079 downregulates the expression of ABA signaling genes, such as OsABF2, OsABF4, OsABI5, and OsNAP. Taken together, these results demonstrate that OsbHLH079 functions in delaying leaf yellowing by attenuating the ABA responses.

Spliceosomal protein U2B″ delays leaf senescence by enhancing splicing variant JAZ9β expression to attenuate jasmonate signaling in Arabidopsis

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.

Arabidopsis BBX14 negatively regulates nitrogen starvation- and dark-induced leaf senescence

Senescence is a highly regulated process driven by developmental age and environmental factors. Although leaf senescence is accelerated by nitrogen (N) deficiency, the underlying physiological and molecular mechanisms are largely unknown. Here, we reveal that BBX14, a previously uncharacterized BBX-type transcription factor in Arabidopsis, is crucial for N starvation-induced leaf senescence. We find that inhibiting BBX14 by artificial miRNA (amiRNA) accelerates senescence during N starvation and in darkness, while BBX14 overexpression (BBX14-OX) delays it, identifying BBX14 as a negative regulator of N starvation- and dark-induced senescence. During N starvation, nitrate and amino acids like glutamic acid, glutamine, aspartic acid, and asparagine were highly retained in BBX14-OX leaves compared to the wild type. Transcriptome analysis showed a large number of senescence-associated genes (SAGs) to be differentially expressed between BBX14-OX and wild-type plants, including ETHYLENE INSENSITIVE3 (EIN3) which regulates N signaling and leaf senescence. Chromatin immunoprecipitation (ChIP) showed that BBX14 directly regulates EIN3 transcription. Furthermore, we revealed the upstream transcriptional cascade of BBX14. By yeast one-hybrid screen and ChIP, we found that MYB44, a stress-responsive MYB transcription factor, directly binds to the promoter of BBX14 and activates its expression. In addition, Phytochrome Interacting Factor 4 (PIF4) binds to the promoter of BBX14 to repress BBX14 transcription. Thus, BBX14 functions as a negative regulator of N starvation-induced senescence through EIN3 and is directly regulated by PIF4 and MYB44.

Histone variant HTB4 delays leaf senescence by epigenetic control of Ib bHLH transcription factor-mediated iron homeostasis

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.

Recent advances in cellular degradation and nuclear control of leaf senescence

Senescence is the final stage of plant growth and development, and is a highly regulated process at the molecular, cellular, and organismal levels. When triggered by age, hormonal, or environmental cues, plants actively adjust their metabolism and gene expression to execute the progression of senescence. Regulation of senescence is vital for the reallocation of nutrients to sink organs, to ensure reproductive success and adaptations to stresses. Identification and characterization of hallmarks of leaf senescence are of great importance for understanding the molecular regulatory mechanisms of plant senescence, and breeding future crops with more desirable senescence traits. Tremendous progress has been made in elucidating the genetic network underpinning the metabolic and cellular changes in leaf senescence. In this review, we focus on three hallmarks of leaf senescence - chlorophyll and chloroplast degradation, loss of proteostasis, and activation of senescence-associated genes (SAGs), and discuss recent findings of the molecular players and the crosstalk of senescence pathways.

Wheat VQ Motif-Containing Protein VQ25-A Facilitates Leaf Senescence via the Abscisic Acid Pathway

Leaf senescence is an important factor affecting the functional transition from nutrient assimilation to nutrient remobilization in crops. The senescence of wheat leaves is of great significance for its yield and quality. In the leaf senescence process, transcriptional regulation is a committed step in integrating various senescence-related signals. Although the plant-specific transcriptional regulation factor valine-glutamine (VQ) gene family is known to participate in different physiological processes, its role in leaf senescence is poorly understood. We isolated TaVQ25-A and studied its function in leaf senescence regulation. TaVQ25-A was mainly expressed in the roots and leaves of wheat. The TaVQ25-A-GFP fusion protein was localized in the nuclei and cytoplasm of wheat protoplasts. A delayed senescence phenotype was observed after dark and abscisic acid (ABA) treatment in TaVQ25-A-silenced wheat plants. Conversely, overexpression of TaVQ25-A accelerated leaf senescence and led to hypersensitivity in ABA-induced leaf senescence in Arabidopsis. A WRKY type transcription factor, TaWRKY133, which is tightly related to the ABA pathway and affects the expression of some ABA-related genes, was found to interact with TaVQ25-A both in vitro and in vivo. Results of this study indicate that TaVQ25-A is a positive regulator of ABA-related leaf senescence and can be used as a candidate gene for wheat molecular breeding.

Plant Hormone Modularity and the Survival-Reproduction Trade-Off

Biological modularity refers to the organization of living systems into separate functional units that interact in different combinations to promote individual well-being and species survival. Modularity provides a framework for generating and selecting variations that can lead to adaptive evolution. While the exact mechanisms underlying the evolution of modularity are still being explored, it is believed that the pressure of conflicting demands on limited resources is a primary selection force. One prominent example of conflicting demands is the trade-off between survival and reproduction. In this review, we explore the available evidence regarding the modularity of plant hormones within the context of the survival-reproduction trade-off. Our findings reveal that the cytokinin module is dedicated to maximizing reproduction, while the remaining hormone modules function to ensure reproduction. The signaling mechanisms of these hormone modules reflect their roles in this survival-reproduction trade-off. While the cytokinin response pathway exhibits a sequence of activation events that aligns with the developmental robustness expected from a hormone focused on reproduction, the remaining hormone modules employ double-negative signaling mechanisms, which reflects the necessity to prevent the excessive allocation of resources to survival.

Delaying or promoting? Manipulation of leaf senescence to improve crop yield and quality

MAIN CONCLUSION

Senescence influences leaf productivity through two aspects: photosynthesis and nutrient remobilization. Through distinctively manipulating progress of leaf senescence, it is promising to improve crop yield and quality simultaneously. Crop yield and quality are two chief goals pursued in agricultural and horticultural production. The basis of crop yield is leaf photosynthesis. Senescence is the last stage of leaf development, which usually causes decreasing of leaf photosynthetic activity. Delaying leaf senescence through physiological or molecular strategies may result in higher photosynthetic activity with a longer duration, thus producing more photoassimilates for biomass accumulation. On the other side, leaf senescence always induces degradation of macromolecular nutrients (including chlorophylls and proteins), and nutritional elements in leaves are then resorbed for development of other organs. For those crops with non-leaf organs as harvested biomass, translocating nutritional elements from leaves to harvested biomass is an indispensable physiological process to increase crop yield and quality. This review summarized successful studies about effects of delaying or promoting senescence on crop yield or quality improvement. Considering the distinctiveness of various crops, manipulation of leaf senescence should be specialized during agricultural and horticultural practices. Rational regulation of leaf senescence, such as inhibiting senescence to maintain leaf photosynthesis and then promoting senescence (with appropriate onset and efficiency) to remobilize more nutrients from leaves to target organs, may ultimately improve both crop yield and quality.

Transcriptomic Analysis of Three Differentially Senescing Maize (Zea mays L.) Inbred Lines upon Heat Stress

Maize, one of the world's major food crops, is facing the challenge of rising temperature. Leaf senescence is the most significant phenotypic change of maize under heat stress at the seedling stage, but the underlying molecular mechanism is still unknown. Here, we screened for three inbred lines (PH4CV, B73, and SH19B) that showed differentially senescing phenotypes under heat stress. Among them, PH4CV showed no obviously senescing phenotype under heat stress, while SH19B demonstrated a severely senescing phenotype, with B73 being between the two extremes. Subsequently, transcriptome sequencing showed that differentially expressed genes (DEGs) were generally enriched in response to heat stress, reactive oxygen species (ROS), and photosynthesis in the three inbred lines under heat treatment. Notably, ATP synthesis and oxidative phosphorylation pathway genes were only significantly enriched in SH19B. Then, the expression differences of oxidative phosphorylation pathways, antioxidant enzymes, and senescence-related genes in response to heat stress were analyzed in the three inbred lines. In addition, we demonstrated that silencing ZmbHLH51 by virus-induced gene silencing (VIGS) inhibits the heat-stress-induced senescence of maize leaves. This study helps to further elucidate the molecular mechanisms of heat-stress-induced leaf senescence at the seedling stage of maize.