Journal of Experimental Botany最新文献

The optimal timing of the transition from vegetative growth to reproductive growth is critical for plant reproductive success, and the underlying regulatory mechanisms have been well studied in angiosperm model species, but relatively little in gymnosperms. DAL1, a MADS domain transcription factor (TF) that shows a conserved age-related expression profile in conifers, may be an age timer. However, how DAL1 mediates the onset of reproductive growth remains poorly understood. Here, we showed that PtDAL1 directly regulates PtDAL10 transcription by binding to its promoter region in vitro. Both in vitro and in Nicotiana benthamiana PtDAL1 forms ternary complexes with PtDAL10 and PtMADS11, two potential candidate regulators of the vegetative to reproductive transition in Chinese pine (Pinus tabuliformis). In new shoots PtDAL10 was progressively induced with age and was also expressed in male and female cones. Overexpression of PtDAL10 rescued the flowering of ft-10 and soc1-1-2 mutants in Arabidopsis. We provide insights into the molecular components associated with PtDAL1, which integrates the vegetative to reproductive phase transition into age-mediated progressive development of the whole plant in conifers.

Biosynthesis of the phytoalexins scopoletin and scopolin in Nicotiana species is regulated by upstream signals including jasmonate (JA), ethylene (ET), and NaWRKY3 in response to the necrotrophic fungus Alternaria alternata, which causes brown spot disease. However, how these signals are coordinated to regulate these phytoalexins remains unknown. By analyzing RNA sequencing data and RNAi, we identified NaERF1B-like (NaERF1B-L) as a key player in Nicotiana attenuata during A. alternata infection by regulating the transcripts of Feruloyl-CoA 6'-hydroxylase 1 (NaF6'H1), encoding a key enzyme for scopoletin biosynthesis, and NaVS1-like (NaVS1-L), a putative biosynthetic gene of the phytoalexin solavetivone. We further demonstrated that the synergistic induction of these two genes by JA and ET signaling is mediated by NaERF1B-L. Additionally, we found that the two closely related proteins, NaWRKY6 and NaWRKY3, physically interact to enhance NaERF1B-L expression by directly binding to and activating the NaERF1B-L promoter. Collectively, our current results demonstrate that NaERF1B-L plays a positive role in resistance to A. alternata by modulating phytoalexin biosynthesis through the integration of JA/ET and NaWRKY6/3 signaling. Our findings reveal a fine-tuned transcriptional regulatory hierarchy mediated by NaERF1B-L for brown spot disease resistance in wild tobacco.

Lichens are a mutualistic symbiosis between a fungus and one or more photosynthetic partners. They are photosynthetically active during desiccation down to relative water contents (RWCs) as low as 30% (on dry mass). Experimental evidence suggests that during desiccation, the photobionts have a higher hydration level than the surrounding fungal pseudo-tissues. Explosive cavitation events in the hyphae might cause water movements towards the photobionts. This hypothesis was tested in two foliose lichens by measurements of ultrasonic acoustic emissions (UAEs), a method commonly used in vascular plants but never in lichens, and by measurements of PSII efficiency, water potential, and RWC. Thallus structural changes were characterized by low-temperature scanning electron microscopy. The thalli were silent between 380% and 30% RWCs, when explosive cavitation events should cause movements of liquid water. Nevertheless, the thalli emitted UAEs at ~5% RWC. Accordingly, the medullary hyphae were partially shrunken at ~15% RWC, whereas they were completely shrunken at <5% RWC. These results do not support the hypothesis of hyphal cavitation and suggest that the UAEs originate from structural changes at hyphal level. The shrinking of hyphae is proposed as an adaptation to avoid cell damage at very low RWCs.

Plant cell walls delimit plant cells from their environment and provide mechanical stability to withstand internal turgor pressure as well as external influences. Environmental factors can be beneficial or harmful for the plants and vary substantially depending on prevailing combinations of climate conditions and stress exposure. Consequently, the physicochemical properties of plant cell walls need to be adaptive, and their functional integrity needs to be monitored by the plant. One major threat to plants is posed by phytopathogens, which employ a diversity of infection strategies and lifestyles to colonise host tissues. During these interactions, the plant cell wall represents a barrier that impedes the colonisation of host tissues and pathogen spread. In a tussle over maintenance and breakdown, plant cell walls can be rapidly and efficiently remodelled by enzymatic activities of plant and pathogen origin, heavily influencing the outcome of plant-pathogen interactions. We review the role of locally and systemically induced cell wall remodelling and the importance of tissue-dependent cell wall properties for the interaction with pathogens. Furthermore, we discuss the importance of cell wall-dependent signalling for defence response induction and the influence of abiotic factors on cell wall integrity and cell wall-associated pathogen resistance mechanisms.

Flavonols are important secondary metabolites that enable plants to resist environmental stresses. Although MYB regulation of flavonol biosynthesis has been well studied, the lncRNA-MYB networks involved in regulating flavonol biosynthesis remain unknown. Ginkgo biloba is rich in flavonols, which are the most important medicinal components. Based on multi-omics data and phylogenetic trees, we identified GbMYB11 as a potential key transcription factor regulating flavonol biosynthesis. Overexpression and VIGS experiments confirmed that GbMYB11 acts as a pivotal positive regulator in flavonol biosynthesis. In the transcriptome of calli overexpressing GbMYB11, we identified significant upregulation of GbF3'H and GbFLS in the flavonol biosynthetic pathway. Yeast one-hybrid and dual-luciferase assays demonstrated that GbMYB11 enhances the expression of GbF3'H and GbFLS by binding to their promoters. Interestingly, we identified LncNAT11, an antisense lncRNA complement to GbMYB11, which negatively regulates flavonol biosynthesis by repressing the expression of GbMYB11. Consequently, we established the LncNAT11-GbMYB11-GbF3'H/GbFLS module as a critical regulator of flavonol biosynthesis in G. biloba, and further elucidated that this module can mitigate the accumulation of reactive oxygen species by modulating flavonol biosynthesis during salt stress. These findings unveil a novel mechanism underlying flavonol biosynthesis and a lncRNA-MYB mediated salt stress tolerance strategy in plants.

Rice HRS1 HOMOLOG3 (OsHHO3) acts as a transcriptional repressor of AMMONIUM TRANSPORTER1 (OsAMT1) genes in rice; thus, reduced OsHHO3 expression in nitrogen (N)-deficient environments promotes ammonium uptake. In this study, we show that OsHHO3 also functions as a repressor of a specific subset of phosphate (Pi) transporter (PT) genes involved in the uptake and root-to-shoot translocation of Pi, including OsPT2, OsPT4, and OsPHO1;1. Consistently, disruption of OsHHO3 increased Pi uptake and Pi contents in shoots and roots, while overexpression of OsHHO3 generated the opposite effects. Furthermore, phosphorus (P) deficiency slightly decreased OsHHO3 expression, upregulating a specific subset of PT genes. However, N deficiency was more effective than P deficiency in suppressing OsHHO3 expression in roots, and unlike N deficiency-dependent activation of PT genes under the control of OsHHO3, the P deficiency-dependent activation of OsAMT1 genes was minimal. Interestingly, the simultaneous deficiency of both N and P promoted the OsHHO3-regulated expression of PT genes more significantly than the deficiency of either N or P, but diminished the expression of genes regulated by OsPHR2, a master regulator of Pi starvation-responsive transcriptional activation. Phenotypic analysis revealed that the inactivation and overexpression of OsHHO3 improved and reduced plant growth, respectively, under N-deficient and P-deficient conditions. These results suggest that OsHHO3 regulates a specific subset of PT genes independently of OsPHR2-mediated regulation and plays a critical role in the adaptation to diverse N and P environments.

Dioecy in flowering plants has evolved independently many different times, and thus the genetic mechanisms underlying sex determination are diverse. In hemp (Cannabis sativa), sex is controlled by a pair of sex chromosomes (XX for females and XY for males). In an attempt to understand the molecular mechanism responsible for sex expression in hemp plants, we carried out RNA-Seq of male and female plants at different developmental stages. Using a pipeline involving differential gene expression analysis and weighted gene co-expression network analysis, we identified genes important for male and female flower development. We also demonstrate that sex-biased expression is already established at very early vegetative stages, before the onset of reproductive development, and several genes encoding transcription factors of the REM, bZIP and MADS family as candidate sex determination genes in hemp. Our findings demonstrate that the gene regulatory networks governing male and female development in hemp diverge already at a very early stage, leading to profound morphological differences in male and female hemp plants.

Nonhost resistance (NHR) is the most durable and robust form of innate immunity, with a surge of interest in crop improvement. Of the NHR genes identified against rice blast, a devastating disease caused by Magnaporthe oryzae, Arabidopsis PEN2 is indispensable for pre-penetration resistance against M. oryzae, while a consortium of genes orchestrates post-penetration resistance via lesser-known mechanisms. We identified M. oryzae-susceptible mosA (mthfr2 pen2-3) from a randomly mutagenized Arabidopsis pen2-3 population using forward genetics. Analysis of T-DNA inserted mthfr2 lines and pen2-3 complemented mosA lines enunciated that MTHFR2-dependent resistance to M. oryzae is independent of PEN2. MTHFR2-defective plants exhibited higher ROS accumulation and expression of SA-dependent defense markers. MTHFR2-ligand docking revealed that A55V nonsynonymous substitution in mosA altered ligand binding efficiency. This further affected the metabolomic profile of mosA, effectively allowing in vitro germination and development of M. oryzae conidia. Moreover, the loss of function mutation in mthfr2 (involved in 1C metabolic pathway) potentiated mosA immunity against Pst DC3000. In conclusion, our findings assert MTHFR2 as a positive modulator of NHR against M. oryzae. This work documents another layer of conserved yet divergent metabolomic defense in Arabidopsis regulated by folate-mediated 1C metabolism that has the potential to revolutionize crop improvement.

The performance of plant hybrids relative to line breeding types is generally associated with higher yields, better adaptation, and improved yield stability. In bread wheat (Triticum aestivum L.), however, a broad commercial success for hybrids has not been accomplished until now largely due to the low efficiency of hybrid grain production, which is highly attributable to its self-pollinating nature. To better understand how hybrid wheat grains can be produced more effectively, we investigated the influence of synchronized flowering between female, i.e. male-sterile, lines and their male cross-pollinator lines as well as of the duration of flowering on hybrid grain production. We found that synchronization of flowering in combination with the longest possible temporal overlap had the largest positive effect on hybrid grain production. However, despite sufficient spatial and temporal synchronization of flowering, we also found that some female lines had lower hybrid grain set than others, suggesting genetic differences in female floral receptivity. To better assess female receptivity, we established a new phenotyping scale of male-sterile wheat flowers that provides the floral basics for effective cross-pollination. Applying this scale in our field and greenhouse trials revealed that better performing female lines remained longer in the pollen-receptive phase.