生命科学最新文献

Polyamines (PAs) along with their conjugated forms, are important mediators of plant defense mechanisms against both biotic and abiotic stresses. Flavin-containing polyamine oxidases (PAOs) regulate PA levels through terminal oxidation. To date, the role of PAOs in plant-herbivore interaction remains poorly understood. We discovered that infestation by the brown planthopper (BPH) disrupts PA homeostasis within the leaf sheaths of rice plants, which co-occurs with the upregulation of OsPAO6, a tissue-specific inducible, apoplast-localized enzyme that regulates the terminal catabolism of spermidine (Spd) and spermine. Functional analysis using CRISPR-Cas9 genome-edited plants revealed that pao6 mutants accumulated significantly higher levels of Spd and phenylpropanoid-conjugated Spd in response to BPH infestation compared to wild-type controls. In addition, BPH feeding on pao6 mutants led to increased honeydew excretion and plant damage by female adults, consistent with in vitro experiments in which Spd enhanced BPH feeding. Furthermore, OsPAO6 transcription is regulated by jasmonate (JA) signaling, and it is dependent on MYC2, which directly binds to the G-box-like motif in the OsPAO6 promoter. Our findings reveal an important role of OsPAO6 in regulating polyamine catabolism in JA-induced responses triggered by herbivore attacks in rice.

Citral, a naturally occurring acyclic monoterpene aldehyde, is present in the essential oils of various plants, but only a few produce it in abundance. Despite its importance as a key aroma molecule, knowledge regarding the in-planta biosynthesis of citral and its metabolic origin remains limited. Here, we have elucidated the functions of an alcohol dehydrogenase (CfADH1) and an aldoketo-reductase (CfAKR2b) in citral biosynthesis in lemongrass (Cymbopogon flexuosus), one of the most cultivated aromatic crops for its citral-rich essential oil. Expression of both CfADH1 and CfAKR2b showed correlation with citral accumulation in different developmental stages. Recombinant CfADH1 and CfAKR2b, despite their sequence unrelatedness, catalyzed citral formation from geraniol with NADP cofactor. Virus-induced gene silencing in lemongrass and transient expression in lemon balm (Melissa officinalis) demonstrated the in-planta involvement of CfADH1 and CfAKR2b in citral biosynthesis. While CfADH1 exhibited a dual cytosolic/plastidial localization, CfAKR2b was localized to the cytosol. This was supported by higher citral-forming activity in the cytosolic fraction than in the chloroplast fraction of lemongrass leaf extract. Moreover, feeding lemongrass seedlings with inhibitors specific to the cytosolic mevalonate pathway and the plastidial methylerythritol phosphate pathway, combined with volatile profiling, supported the involvement of both pathways in citral formation. Taken together, our results indicate that high citral production has evolved in lemongrass through the recruitment of phylogenetically distant enzymes localized in both the cytosol and plastids.

Among flowering plants, genome size varies remarkably, by >2200-fold, and this variation depends on the loss and gain of noncoding DNA sequences that form distinct heterochromatin complexes during interphase. In plants with giant genomes, most chromatin remains condensed during interphase, forming a dense network of heterochromatin threads called interphase chromonemata. Using super-resolution light and electron microscopy, we studied the ultrastructure of chromonemata during and after replication in root meristem nuclei of Nigella damascena L. During S-phase, heterochromatin undergoes transient decondensation locally at DNA replication sites. Due to the abundance of heterochromatin, the replication leads to a robust disassembly of the chromonema meshwork and a general reorganization of the nuclear morphology visible even by conventional light microscopy. After replication, heterochromatin recondenses, restoring the chromonema structure. Thus, we show that heterochromatin replication in interphase nuclei of giant-genome plants induces a global nuclear reorganization.

Lotus (Nelumbo nucifera G.) is a perennial aquatic horticultural plant with diverse architectures. Distinct plant architecture (PA) has certain attractive and practical qualities, but its genetic morphogenesis in lotus remains elusive. In this study, we employ genome-wide association analysis (GWAS) for the seven traits of petiole length (PLL), leaf length (LL), leaf width (LW), peduncle length (PLF), flower diameter (FD), petal length (PeL), and petal width (PeW) in 301 lotus accessions. A total of 90 loci are identified to associate with these traits across 4 years of trials. Meanwhile, we perform RNA sequencing (RNA-seq) to analyze the differential expression of the gene (DEG) transcripts between large and small PA (LPA and SPA) of lotus stems (peduncles and petioles). As a result, eight key candidate genes are identified that are all primarily involved in plant cell wall remodeling significantly associated with PA traits by integrating the results of DEGs and GWAS. To verify this result, we compare the cell wall compositions and structures of LPA versus SPA in representative lotus germplasms. Intriguingly, compared with the SPA lotus, the LPA varieties have higher content of cellulose and hemicellulose, but less filling substrates of pectin and lignin. Additionally, we verified longer cellulose chains and higher cellulose crystallinity with less interference in LPA varieties. Taken together, our study illustrates how plant cell wall remodeling affects PA in lotus, shedding light on the genetic architecture of this significant ornamental trait and offering a priceless genetic resource for future genomic-enabled breeding.

Fiber elongation rate is an essential characteristic of cotton fiber in the textile industry, yet it has been largely overlooked in genetic studies. Gibberellins (GAs) and auxin (IAA) are recognized for their role in directing numerous developmental processes in plants by influencing cell differentiation and elongation. However, the degree to which GA-IAA interaction governs cellular elongation in cotton fiber cells remains to be fully understood. In this study, we identified a causal gene, Gibberellic Acid-Stimulated in Arabidopsis 24 (GhGASA24), that appears to be responsible for fiber elongation rate via regulating fiber cell wall thickness. Subsequent experiments revealed that GhGASA24 influences cell wall formation by promoting the expression of GhCesA8 and GhCesA10. Our findings suggest that Auxin Response Factor 2 (GhARF2) regulates fiber elongation rate by directly binding to the AuxRE elements in GhGASA24 promoter. In addition, we identified Growth Regulation Factor 4 (GhGRF4) as a transcription factor that interacts with GhARF2 to form a heterodimer complex, which also transcriptionally activates GhGASA24. Intriguingly, GhGRF4 regulates GhARF2 expression by directly binding to its promoter, thereby acting as a cascade regulator to enhance the transcriptional levels of GhGASA24. We propose that the GhGRF4/GhARF2-GhGASA24-GhCesAs module may contribute to fiber cell wall thickness by modulating cellulose biosynthesis, and provide a theoretical basis for improvement of fiber quality.

A series of polyploidizations in higher-order polyploids is the main event affecting gene content in a genome. Each polyploidization event can lead to massive functional divergence because of the subsequent decrease in selection pressure on duplicated genes; however, the causal relationship between multiple rounds of polyploidization and the functional divergence of duplicated genes is poorly understood. We focused on the Triticum-Aegilops complex lineage and compared selection pressure before and after tetraploidization and hexaploidization events. Although both events led to decreased selection pressure on homoeologous gene pairs (compared with diploids and tetraploids), the initial tetraploidization had a greater impact on selection pressure on homoeologous gene pairs than did subsequent hexaploidization. Consistent with this, selection pressure on expression patterns for the initial event relaxed more than those for the subsequent event. Surprisingly, the decreased selection pressure on these homoeologous genes was independent of the existence of in-paralogs within the same subgenome. Wheat homoeologous pairs had different evolutionary consequences compared with orthologs related to other mechanisms (ancient allopolyploidization, ancient autopolyploidization, and small-scale duplication). Furthermore, tetraploidization and hexaploidization also seemed to have different evolutionary consequences. This suggests that homoeologous genes retain unique functions, including functions that are unlikely to be preserved in genes generated by the other duplication mechanisms. We found that their unique functions differed between tetraploidization and hexaploidization (e.g., reproductive and chromosome segregation processes). These findings imply that the substantial number of gene pairs resulting from multiple allopolyploidization events, especially initial tetraploidization, may have been a unique source of functional divergence.

C₄ species have evolved more than 60 times independently from C₃ ancestors. This multiple and parallel evolution of the complex C₄ trait suggests common underlying evolutionary mechanisms, which could be identified by comparative analysis of closely related C₃ and C₄ species. Efficient C₄ function depends on a distinctive leaf anatomy that is characterised by enlarged, chloroplast-rich bundle sheath cells and narrow vein spacing. To elucidate the molecular mechanisms that generate the Kranz anatomy, we analysed a developmental series of leaves from the C₄ plant Flaveria bidentis and the closely related C₃ species Flaveria robusta by comparing anatomies and transcriptomes. Vascular density measurements of all nine leaf developmental stages identified three leaf anatomical zones whose proportions vary with respect to the developmental stage. We then deconvoluted the transcriptome datasets using non-negative matrix factorisation, which identified four distinct transcriptome patterns in the growing leaves of both species. By integrating the leaf anatomy and transcriptome data, we were able to correlate the different transcriptional profiles with different developmental zones in the leaves. These comparisons revealed an important role for auxin metabolism, in particular auxin homeostasis (conjugation and deconjugation), in establishing the high vein density typical of C₄ species.

Pustule formation is pivotal for the development of the Xanthomonas citri subsp. citri (Xcc)-induced citrus canker disease (CCD). Although our previous study demonstrated that the exogenous application of abscisic acid (ABA) facilitated pustule formation induced by Xcc, the precise mechanism remains elusive. The 9-cis-epoxycarotenoid dioxygenase (NCED) is a crucial enzyme in ABA biosynthesis. This study explored the role of citrus CsNCED1-1 in CCD resistance through overexpression and RNA interference of CsNCED1-1 in Wanjincheng orange (Citrus sinensis). Our findings indicated that CsNCED1-1 negatively modulated CCD resistance by fostering ABA accumulation, concomitant with an increase in jasmonic acid (JA) and a decrease in salicylic acid (SA). Plants overexpressing CsNCED1-1 displayed shortened leaves with smaller and denser stomata along with irregular and increased palisade cells. CsLOB1 is a known susceptibility gene for CCD, and CsbZIP40 positively influences resistance to this disease. We further confirmed that CsLOB1 promoted and CsbZIP40 suppressed the transcription of CsNCED1-1 by directly binding to the CsNCED1-1 promoter. Notably, CsbZIP40 and CsLOB1 showed a competitive relationship in the regulation of CsNCED1-1 expression, with CsbZIP40 exhibiting greater competitiveness. Overall, our findings highlight that CsNCED1-1 promotes susceptibility to citrus canker by disrupting JA- and SA-mediated defense mechanisms and triggering the proliferation and remodeling of palisade cells, thereby facilitating pathogen colonization and pustule formation. This study offers novel insights into the regulatory mechanisms underlying citrus canker resistance and the role of CsNCED1-1 in citrus.

Plant-specialized metabolism represents an inexhaustible source of active molecules, some of which have been used in human health for decades. Among these, monoterpene indole alkaloids (MIAs) include a wide range of valuable compounds with anticancer, antihypertensive, or neuroactive properties. This is particularly the case for the pachysiphine derivatives which show interesting antitumor and anti-Alzheimer activities but accumulate at very low levels in several Tabernaemontana species. Unfortunately, genome data in Tabernaemontanaceae are lacking and knowledge on the biogenesis of pachysiphine-related MIAs in planta remains scarce, limiting the prospects for the biotechnological supply of many pachysiphine-derived biopharmaceuticals. Here, we report a raw version of the toad tree (Tabernaemontana elegans) genome sequence. These new genomic resources led to the identification and characterization of a couple of genes encoding cytochrome P450 with pachysiphine synthase activity. Our phylogenomic and docking analyses highlight the different evolutionary processes that have been recruited to epoxidize the pachysiphine precursor tabersonine at a specific position and in a dedicated orientation, thus enriching our understanding of the diversification and speciation of the MIA metabolism in plants. These gene discoveries also allowed us to engineer the synthesis of MIAs in yeast through the combinatorial association of metabolic enzymes resulting in the tailor-made synthesis of non-natural MIAs. Overall, this work represents a step forward for the future supply of pachysiphine-derived drugs by microbial cell factories.

Atherosclerosis is one of the important diseases of the circulatory system because atherosclerotic plaques cause significant disruption of blood flow. Therefore, it is very important to properly understand these processes and skillfully simulate blood flow. In our work, we consider blood flow through an abdominal aorta with iliac arteries, assuming that the right iliac artery is narrowed by an atherosclerotic lesion. Blood flow is simulated using the laminar, standard $k-\omega$ and standard $k-ϵ$ models. The obtained results show that despite the use of identical initial conditions, the distribution of velocity flow and wall shear stress depends on the choice of flow simulation model. For the $k-ϵ$ model, we obtain higher values of speed and wall shear stress on atherosclerotic plaque than in the other two models. The laminar and $k-\omega$ models predict larger areas where reverse blood flow occurs in the area behind the atherosclerotic lesion. This effect is associated with negative wall shear stress. These two models give very similar results. The results obtained by us, and those reported in the literature, indicate that $k-\omega$ model is the most suitable for blood flow analysis.