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Leaves, the primary carbon fixers in autotrophic plants, undergo a complex senescence process, which is critical for the redistribution of nutrients and supports ongoing growth and development. This natural aging phenomenon, often triggered at the end of a plant's life cycle or during the autumn season in perennial species, is finely regulated at multiple levels. Premature senescence can disrupt normal plant development, while the timing and pace of senescence significantly impact crop yield and quality. Notably, accelerated senescence under stress conditions may enhance the survival of future generations, suggesting an evolutionary strategy for plants to cope with harsh environments. Our review focuses on the molecular regulation of leaf senescence in woody plants, emphasizing the intricate determinants and regulatory mechanisms involved, including the role of phytohormones, environmental cues and genetic factors. We highlight recent advances in understanding the regulation of leaf senescence in woody plants, integrating insights from multidisciplinary approaches and cutting-edge technologies. [ABSTRACT FROM AUTHOR]

Summary: 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. See also the Commentary on this article by Dubos, 240: 461–463. [ABSTRACT FROM AUTHOR]

Complex organic aerosols in the upper atmosphere of Saturn's moon Titan reach the troposphere and surface, where a methane (CH4)‐based hydrological cycle occur. Previous studies have assumed no interactions between organic aerosols and liquid CH4, although the dissolution of low‐molecular‐weight photochemical products in liquid CH4 has been considered. Here we report experimental results of soaking a laboratory analog (so‐called tholin) of Titan's organic aerosols in liquid CH4 at 93–98 K for several hours and then evaporating the liquid, simulating wet–dry cycling on Titan. After wet–dry cycling, residual tholin particles form aggregates through cementation. Solid evaporitic deposits formed by evaporation of interacted liquid contain nitrogen‐bearing aromatics, suggesting selective dissolution of aromatics. Our results suggest that organic aerosols or high‐molecular‐weight compounds adsorbed on them partly dissolve in liquid CH4 on Titan, even during short‐term wetting events, promoting the growth of aerosols to dune particles via aggregation and providing aromatics to evaporites. Plain Language Summary: Saturn's largest moon, Titan has a dense atmosphere composed of nitrogen and methane. Active organic chemistry induced by sunlight occurs in the atmosphere to form complex organic aerosols. These organic aerosols eventually settle on the surface, where rivers, lakes, and seas of liquid methane are present. Upon seasonal changes in precipitation and evaporation, wet–dry cycling of liquid methane is believed to occur on Titan, similar to Earth's water cycles. Can organic aerosols settled on the surface be dissolved into liquid methane? If so, what components of aerosol can be dissolved, and how could this affect Titan's geology? Here we perform laboratory experiments to address these questions. Unlike predictions by previous studies, we find that organic aerosols or aromatics adsorbed on them would partly dissolve into liquid methane efficiently. These processes could play key roles in the formation of unique landforms, such as dunes and evaporites, on Titan. Key Points: We experimentally simulate interactions between laboratory analogs (tholin) of Titan's aerosols and liquid methane at low temperaturesComplex aromatics are dissolved from tholin, forming evaporites after drying; while, residual tholin form aggregatesWet–dry cycling of aerosols on Titan may provide aromatics to evaporites and could explain size growth of aerosols to dune particles [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]