New Phytologist最新文献

Although the cell cycle is conserved between plants and other eukaryotes, there are also significant differences, particularly in G2 regulation. In particular, the WEE1/CELL DIVISION CYCLE25 (CDC25) circuit that establishes G2 timing in animals and fungi is absent in plants. In Arabidopsis thaliana, SIAMESE (SIM), a well-known regulator of endoreplication with homologs throughout land plants, is a cyclin-dependent kinase (CDK) inhibitor that restricts progression through mitosis. Mathematical modeling indicated that SIM may modulate the length of G2 during mitotic cycles in addition to its role in endoreplication. This prediction was tested several ways. First, root growth of sim lagged slightly behind that of wild-type (WT) and the root meristem was longer in sim than in WT. Second, two independent methods of monitoring cell cycle phases, long-term live-cell imaging and 5-ethynyl-2-deoxyuridine (EdU) pulse-chase labeling, showed that G2 is shorter in sim root meristem cortex cells than in WT. Finally, fluorescence levels of a CYCB:GFP fusion that responds directly to G2 CDK activity were consistent with sim mutants having greater G2 CDK activity. These results suggest that, in addition to its role in endoreplication, SIM plays a role in determining the length of G2 during mitotic cycles, potentially substituting in part for the functions of WEE1/CDC25.

Although nitrogen (N) enrichment and precipitation changes are known to influence plant phenology and reproduction via altered soil nutrient and water availability, as well as above- and belowground biological processes, how these phenological changes affect reproduction remains unclear. Based on a field experiment with N addition and altered precipitation conducted in an alpine meadow on the eastern Tibetan Plateau since 2020, we explored their effects on plant reproductive phenology, reproductive output, and success from 2023 to 2024. N addition delayed the reproductive period, reduced the flowering asynchrony, and decreased both flower and fruit production in alpine plants. Notably, the interactive effects of N and precipitation addition significantly enhanced fruit set. Phenological shifts mediated plant reproductive responses to N addition and altered precipitation. Specifically, while N addition directly decreased flower and fruit production, it indirectly enhanced fruit set via phenological changes (including the peak flowering and the start of fruiting). These findings highlight the critical role of phenology in mediating alpine plant reproduction responses to N enrichment. Although delayed reproductive phenology enhances fruit set in alpine plants, its compensatory effect on N-induced reproductive losses remains limited under continuous nitrogen enrichment.

The Chrysanthemum genus (Asteraceae) is a key polyploidy model, but its complex genomes obscure its origin and evolution. To address this, we developed chromosome-set-specific painting probes from the Chrysanthemum morifolium 'Zhongshanzigui' haploid genome, enabling precise identification of all nine chromosome sets. Combined with existing oligonucleotide probes (Oligo-Mix: CmOP-1 and CmOP-2), we established a novel sequential fluorescence in situ hybridization (FISH) procedure for comparative genomic analysis. Applying this across six Chrysanthemum species revealed extraordinarily conserved chromosomal synteny. Analysis of diploids (e.g. C. nankingense, C. lavandulifolium, and C. indicum) and their derived autotetraploids showed autopolyploidization involved amplification of large-scale repetitive sequences and loss of partial repeats. Crucially, rapid cytological diploidization (diploid-like bivalent pairing) occurred, associated with significant enrichment of repetitive sequences at meiotic crossover (CO) loci on homologous chromosomes. This leads us to hypothesize that repetitive DNA variation may facilitate precise chromosome segregation and diploid-like meiosis, thereby potentially ensuring polyploid stability. These findings provide essential tools for distinguishing homologous chromosomes and significant potential for elucidating homologous interactions to advance polyploid Chrysanthemum breeding.

In plants, the process of state transition regulates the allocation of sunlight energy between Photosystem II (PSII) and PSI. However, the implications of state transitions for harmonizing electron transport rates between photosystems, and a full quantitative picture of this process, remain underexplored. We integrated quantitative biology (biochemical and biophysical approaches) with in vivo spectroscopy on wild-type Arabidopsis and protein phosphorylation mutants. This combination facilitated monitoring of Chl redistribution and its functional implications for light harvesting and electron transport. Our findings demonstrate the reallocation of 12% of highly phosphorylated 'extra' light-harvesting complex II under state 2 from stacked to unstacked thylakoids. This reduces the number of Chls per PSII from 216 to 182, while increasing the number in PSI from 187 to 223. Such Chl redistribution compensates for differences in photosystem stoichiometry and photochemical quantum efficiencies, thereby precisely synchronizing electron transport rates in both photosystems. Mutant analyses corroborate that this regulatory mechanism involves reversible phosphorylation. We inferred that state transitions optimize linear electron transport, leaving no additional capacity for cyclic electron transport. Furthermore, the results suggest that the controversies about long-range migration of LHCII from stacked to unstacked thylakoid domains arise from differences in phosphorylation levels.

Demographic compensation occurs when reductions in some vital rates are offset by increases in others, allowing populations to maintain similar performance across varying environments. This mechanism may help explain species' ecological distributions and range limits, yet its role at microenvironmental scales remains poorly understood. We investigated demographic compensation in Ipomoea cavalcantei, a narrow-range but locally abundant species endemic to Amazonian ironstone outcrops, by comparing populations in two contrasting habitats: open- and shrubby-canga. Using 3 yr of demographic data, we built matrix population models and conducted a life table response experiment. We also carried out germination and seedling establishment experiments under different temperature and light conditions simulating both habitats to identify the potential environmental drivers and their effects on key life-cycle events. Despite contrasting environmental conditions, both populations exhibited similar population growth rates (λ), with opposing contributions of growth and fecundity - evidence of demographic compensation. The open-canga population had lower growth but higher recruitment, driven by favorable temperature regimes for seed dormancy release and germination. Reduced growth was associated with physiological stress under high irradiance and shallow soils. Our results show that demographic compensation allows I. cavalcantei to persist across microhabitats, highlighting the importance of fine-scale environmental heterogeneity in shaping species distributions.

In eukaryotes, XERODERMA PIGMENTOSUM GROUP D (XPD) is an integral subunit of the DNA repair/transcription complex TFIIH. In animals, XPD has been implicated in TFIIH-independent complexes regulating cell division, which, however, remains poorly understood in plants. Here, we identified XPD as a novel regulator of stomatal development in Arabidopsis. Its loss-of-function mutants exhibited increased stomatal precursor cells and formed stomatal clusters. Genetic analysis showed that XPD functions upstream of SPEECHLESS (SPCH) to control stomatal lineage entry, coordinates with MUTE to regulate meristemoid division and works together with FLP and FAMA to restrict GMC division. In a search of XPD interactors, we identified CDKA;1, which serves as both an essential cyclin-dependent kinase and a key SPCH activator. Consistently, xpd mutants exhibited enhanced stomatal lineage cell divisions and elevated SPCH protein levels. Furthermore, XPD acts upstream of CDKA;1, as expression of the dominant-negative CDKA;1.N146 allele significantly suppressed the excessive cell division and stomatal development defects in xpd plants. Our data highlight the precise regulation of stomatal development by XPD, expanding its critical TFIIH-independent roles in plant cell division and fate specification.

In Arabidopsis, stomatal patterning is directed by receptor complexes involving the ERECTA-family (ERf) and SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) proteins. The endosomal sorting complex required for transport (ESCRT) facilitates endocytic degradation of membrane proteins, while its specific role in modulating stomatal patterning remains elusive. Here, we show that the ESCRT-III-associated proteins VPS46.1 and VPS46.2 function redundantly to govern stomatal patterning. Loss of VPS46 function leads to excessive, disorganized stomatal lineage divisions and clustering. Genetic analyses position VPS46 downstream of EPF2 and upstream of the YODA-Mitogen-Activated Protein Kinase (MAPK) cascade. VPS46 proteins localized to late endosomes and colocalized with ERf receptors. The VPS46 mutation specifically disrupted the vacuolar degradation of the ERf-SERKs complex, terminally trapping the receptors on the tonoplast and halting their further cycling. By contrast, the trafficking and function of the brassinosteroid receptor BRI1 were unaffected. Our study identifies VPS46 as a critical regulator that determines the postendocytic fate of the ERf-SERKs receptor complex. It reveals a novel substrate-selective mechanism within the ESCRT pathway, whereby VPS46 ensures the precise spatial patterning of stomata by facilitating degradation of the ERf-SERKs complex to fine-tune signaling output.

Postharvest pathogens can infect fresh produce both before and after harvest, by direct or wound-enhanced penetration, remaining quiescent until ripening. Biotrophic-like postharvest pathogens persist beneath host cells and can remain in a state of quiescence. They detect environmental cues and regulate quiescence through chromatin-level control and the secretion of effectors that interact with host pattern recognition receptors. By contrast, necrotrophic fungi persist between dead cells and depend more directly on nutrient availability to prime their growth and upon secretion for fungal virulence factors. During quiescence, the host also mounts specific responses, including activation of pattern recognition receptor genes, ethylene signaling (particularly in unripe fruit), and defense genes such as PR-10 and chitinases. Jasmonic acid and ethylene pathways synergistically enhance these defenses. As fruit ripens, the transition from quiescence to active necrotrophic growth is triggered, accelerating tissue decay. This activation is driven by several key factors, including weakened host defenses, decreased levels of antifungal compounds such as polyphenols, increased cell wall accessibility due to fruit softening and ripening-associated changes in signaling pathways, which alter environmental pH, carbon metabolism, and secondary metabolite production. These regulatory mechanisms collectively govern the timing and extent of fungal initiation of colonization during fruit senescence.

Plants lose water by transpiration through stomatal pores. However, it remains a matter of debate whether relative humidity (RH) in the substomatal cavity may fall below saturation and guard cells experience strong differences water potential driven by RH in the cavity. We developed a gas exchange chamber to control RH and CO₂ at the inner epidermal surface. Vicia faba L. stomata remained open with high stomatal conductance (g_s), even when RH inside was reduced substantially below saturation. Concurrent measurements showed no resolvable decline in bulk cell wall water potential, even with 50 %RH inside, provided the wall space was hydrated. Only when the tissue was allowed to dry did the wall water potential fall below -2 MPa, the stomata close, and g_s collapse to values near zero. These findings concurred with OnGuard model predictions showing large decreases in RH in the leaf under water stress. The observations highlight a steady-state flux from liquid in the cell wall to vapour in the substomatal cavity and across the stomatal pore; they implicate cell wall water in shielding the stomata against leaf airspace humidity; and they pose a challenge to consider the kinetics of evaporative flux behind stomatal transpiration.

Over the past century, research has significantly advanced our understanding of fruit respiration, from (eco)physiological processes to molecular mechanisms. This review focuses on the functional relevance and regulatory roles of mitochondrial alternative respiratory pathways (ARPs) during fruit growth and ripening. We revisit classical distinctions between climacteric and nonclimacteric fruits, considering recent insights into the alternative oxidase, uncoupling proteins, and type II NAD(P)H dehydrogenases (NDIIs). These components are increasingly recognized as central to maintaining metabolic flexibility, energy balance, and redox homeostasis, supporting both primary and secondary metabolism. We highlight how CO₂ refixation and organic acid metabolism, often displaying C₄/CAM-like features, impose specific demands on mitochondrial electron transport, and how spatial heterogeneity in metabolism and O₂ availability across fruit tissues can shape respiratory activity. Interactions between fruit photosynthesis and respiration remain poorly understood, particularly under stress. The interplay between respiration, ethylene biosynthesis, and signaling is discussed, emphasizing feedback loops involving mitochondrial retrograde regulation and redox-sensitive control of ripening. Key knowledge gaps include in vivo flux analyses, tissue-resolved energy profiling, and functional characterization of underexplored ARP components. Finally, we outline postharvest and metabolic engineering strategies targeting ARPs as complementary to ethylene-centered approaches to improve fruit quality, stress resilience, and nutritional value.