Publikationen - Stoffwechsel- und Zellbiologie

The Lamiaceae family, the sixth largest among angiosperms, is renowned for its rich diversity of terpenoids, many of which exhibit remarkable bioactivities, including anti-inflammatory, psychoactive, anti-cancer, and antiviral effects. Notable examples with fully elucidated biosynthetic pathways include menthol from peppermint, forskolin from blue spur flower, and carnosol from rosemary. For other key Lamiaceae terpenes—such as the anti-cancer oridonin, the psychoactive salvinorin A, and bioactive marrubiin and vitexilactone—significant progress has been made. This review explores the bioactivity and biosynthesis of Lamiaceae terpenes, with a focus on mono- and diterpenes, while highlighting future research directions.

Background and Aims We have abundant knowledge on drought responses of plants or soil microorganisms individually. However, there is a severe lack of knowledge regarding interactions in the plant-soil-microbiome continuum, and specifically root-soil interface traits including the role of root hairs. Here, we investigated how water limitation propagates in a plant-soil-microbiome system upon stopping irrigation. We used two Zea mays genotypes (rth3 and its isogenic wildtype B73), differing in root hair formation, to elucidate the effect of rhizosphere extension under water limitation. Methods For 22 days, WT and rth3 were grown in a climate chamber, with irrigation stopped for drought treatment during the last 7 days. Daily measurements included soil water status, plant evapotranspiration and gas exchange. At harvest, root exudates, shoot relative water content, osmolality and nutrients, root morphological traits and transcriptomics, and soil microbial β-diversity and enzyme activity were determined. Key Results In line with a larger plant size, drought stress developed more rapidly and the number of differentially expressed genes was higher in the WT compared to rth3. Under water limitation, root exudation rates increased and soil enzyme activities decreased more strongly in the WT rhizosphere. In both genotypes, water level significantly altered microbial β-diversity in the bulk soil, particularly affecting fungi more than bacteria/archaea. The genotype affected only bacteria/archaea and was more pronounced in rhizosphere than in bulk soil.Conclusions This interdisciplinary study assessed how a short drought stress manifested in a plant-soil-microbiome system. Water limitation altered microbial (fungal) diversity more distant from the root surface. Genotype-specific stress-induced increases in exudation rates modified microbial activity in root proximity, possibly pointing to root hair functions under water limitation. Less intense drought responses of rth3 were confirmed at all levels of investigation and may be due at least in part to its smaller plant size.

Plant architecture is a key determinant of crop yield, and understanding the genetic basis of its regulation is crucial for crop improvement. BLADE-ON-PETIOLE (BOP) genes are known to play a fundamental role in shaping plant architecture across diverse species. In this study, we demonstrate pleiotropic effects of the barley BOP gene Uniculme4 (Cul4) on various aspects of plant architecture, including plant height, culm diameter, and grain traits. Accordingly, Cul4 is broadly expressed in different tissues and developmental stages. Comparing transcriptome profiles of cul4 mutant and wild-type plants, we uncover a novel link between Cul4 and the jasmonic acid (JA) biosynthetic pathway. Our findings demonstrate that proper Cul4 function is required to repress JA biosynthesis, with cul4 mutants exhibiting increased levels of JA and its precursor 12-oxo-phytodienoic acid. Up-regulation of WRKY and bHLH transcription factors shows JA signalling is also impacted by Cul4. Additionally, our study sheds light on the role of Cul4 in flowering time regulation, potentially through its interaction with florigen-like genes. This research enhances our understanding of the mechanisms and pathways acting downstream of BOP genes.

Fruit pigmentation is a major signal that attracts frugivores to enable seed dispersal. In most fleshy fruit, green chlorophyll typically accumulates early in development and is replaced by a range of pigments during ripening. In species such as grape and strawberry, chlorophyll is replaced by red anthocyanins produced by the flavonoid biosynthetic pathway. Eggplant (Solanum melongena) is unique, as its fruit accumulates anthocyanins beginning from fruit set, and these are later replaced by the yellow flavonoid-pathway intermediate naringenin chalcone. To decipher the genetic regulation of this extraordinary pigmentation shift, we integrated mRNA and microRNA (miRNA) profiling data obtained from developing eggplant fruit. We discovered that SQUAMOSA PROMOTER BINDING-LIKE (i.e., SPL6a, SPL10, and SPL15), MYB1, and MYB2 transcription factors (TFs) regulate anthocyanin biosynthesis in early fruit development, whereas the MYB12 TF controls later accumulation of naringenin chalcone. We further show that miRNA157 and miRNA858 negatively regulate the expression of SPLs and MYB12, respectively. Taken together, our findings suggest that opposing and complementary expression of miRNAs and TFs controls the pigmentation switch in eggplant fruit skin. Intriguingly, despite the distinctive pigmentation pattern in eggplant, fruit development in other species makes use of homologous regulatory factors to control the temporal and spatial production of different pigment classes.

Plants are naturally subjected to various types of biotic stresses, including pathogenic microorganisms and herbivory by insects, which trigger different signaling pathways and related defense mechanisms. Inoculation with microorganisms, such as plant growth-promoting rhizobacteria (PGPR), can be seen as a form of stress because it triggers a systemic resistance response in plants similar to that caused by insect herbivory. However, these interactions have typically been studied independently, which has limited the understanding of their combined effects. This study examines the effects of Bacillus amyloliquefaciens GB03 inoculation and Spodoptera frugiperda herbivory on the total phenolic contents of Ocimum basilicum. We also analyze the levels of endogenous phytohormones and the activity of phenylalanine ammonia-lyase (PAL), a crucial enzyme involved in the biosynthesis of phenolic defense-related metabolites. The results indicate that the total phenolic content significantly increased only in plants that were both inoculated by GB03 and damaged by larvae. Additionally, PAL activity showed an increase in plants that were damaged by larvae and in those subjected to the combined treatment of larval damage and inoculation with GB03. Regarding phytohormones, in plants damaged by insects, the levels of salicylic acid (SA) increased, regardless of whether they were inoculated or not, while the levels of jasmonic acid–isoleucine (JA-ile) rose in all treatments compared to the control. This study highlights the intricate relationships among beneficial microbes, herbivores, and plant defense mechanisms, emphasizing their potential impact on improving plant resilience and the production of secondary metabolites. Furthermore, understanding the independent effects of PGPR inoculation, beyond its interaction with herbivory, could provide valuable insights into its role as a sustainable alternative for enhancing plant defense responses and promoting crop productivity.

12-cis-oxo-phytodienoic acid (OPDA), a precursor of jasmonoyl-isoleucine (JA-Ile), is known to have distinct signaling roles in Arabidopsis, as shown in studies using the opr3 mutant, which lacks OPDA REDUCTASE3 (OPR3). This mutant, however, accumulates low levels of JA-Ile through an OPR2-mediated bypass. To investigate OPDA signaling, the wound-induced transcriptome of the opr2opr3 mutant is compared to that of wild-type and allene oxide synthase mutant. Endogenous OPDA shows no unique transcriptional signature under control or wounding conditions, and previously identified OPDA-responsive genes are wound-induced independently of OPDA. Applying OPDA to opr2opr3 triggers a distinct response suggesting compartmentalization of endogenously formed OPDA. Trans-organellar complementation reveals that expression of OPR3 or OPR2 in opr2opr3 restores JA-Ile production regardless of localization, whereas mitochondrial targeted OPR1 exhibiting low OPDA/4,5-ddh-JA conversion activity does not. Our findings show that OPDA primarily serves as a JA precursor with limited independent signaling functions in the early wound response.

Main conclusion The DNA-binding protein WHIRLY1, sharing structural similarities with ferritin, plays a role in the formation of iron cofactor proteins within chloroplasts. Abstract Previous studies indicated that barley plants with a knockdown of HvWHIRLY1 containing a minimal amount of the protein are compromised in chloroplast development and photosynthesis, and get chlorotic leaves when grown at high irradiance. Thereby, the leaves display signs of iron deficiency. Metal determination revealed, however, that leaves of WHIRLY1-deficient plants had a regular iron content. Nevertheless, WHIRLY1-deficiency affected the functionality of photosystem II less than that of photosystem I, which has a higher demand for iron. Immunological analyses revealed that components of both photosystems had reduced levels. Additionally, the levels of other chloroplast proteins containing different classes of iron cofactors were lower in the WHIRLY1-deficient plants compared to the wild type. In contrast, the level of the iron sequestering protein ferritin increased in WHIRLY1-deficient lines, whereby high irradiance intensified this effect. RNA analyses showed that the upregulation of ferritin coincided with an enhanced expression of the corresponding gene, reflecting an apparent overload of chloroplasts with free iron. Ferritin and WHIRLY proteins are known to share the same oligomeric structure. Therefore, the high abundance of ferritin in WHIRLY1-deficient plants might be a compensation for the reduced abundance of WHIRLY1. Enhanced expression levels of genes encoding photosynthesis proteins and iron cofactor proteins indicate a demand for protein formation or assembly of protein complexes. The results support a general role of WHIRLY1 in assembly and/or stabilization of chloroplast proteins and, moreover, suggest a specific function in sequestering and supply of iron in chloroplasts.

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This work investigated physiological, biochemical, and molecular adaptive responses of two Egyptian rice cultivars representing two different subspecies, Giza 177 (japonica) and Giza 178 (indica/japonica), to osmo-equivalent concentrations of mannitol and NaCl to mimic drought and salinity stress, respectively. Phenotypically, Giza 178 was less sensitive to drought than Giza 177; however, salt stress generated comparable damage symptoms and sodium content in either variety. In Giza 178, more K+ were accumulated in shoots under drought compared to Giza 177 with a 1.48-fold increase, while Ca++ content was significantly higher in shoots under drought and salt treatments (2 and 1.7-fold increase, respectively). Carbon isotope discrimination (CID) implied a prolonged stomatal closure in Giza 177 under drought. Additionally, the oxidative damage marker malondialdehyde (MDA) was more severely accumulated in Giza 177 shoots with 1.67-fold increase. The antioxidative enzymatic activity of Glutathione Reductase (GR) increased in Giza to 178 shoots under drought, indicating better antioxidative power. Interestingly, OsNHX1 gene expression (Na+/H+ antiporter) was significantly induced in Giza 178 shoots under drought stress, indicating better osmotic turgor pressure and less degree of nutrition deficiency. Furthermore, both phytohormone abscisic acid (ABA) and jasmonate iso-leucine (JA-Ile) were significantly elevated in Giza 177 shoots compared to Giza 178 under drought and salt stress. Generally, it is suggested that Giza 177 shoots displayed greater sensitivity to drought, mainly due to extensive oxidative damage caused by a prolonged period of stomatal closure.

Terpenes, the largest class of plant specialized products, are built from C5 building blocks via terpene synthases and oxidized by cytochrome P450 enzymes (CYPs) for structural diversity. In some cases, CYPs do not simply oxidize the terpene backbone, but induce backbone rearrangements, methyl group shifts, and carbon–carbon (C–C) scissions. Some of these reactions were characterized over 25 years ago, but most of them were reported in recent years, indicating a highly dynamic research area. These reactions are involved in mono-, sesqui-, di- and triterpene metabolism and provide key catalytic steps in the biosynthesis of plant hormones, volatiles, and defense compounds. Many commercially relevant terpenoids require such reaction steps in their biosynthesis such as triptonide (rodent pest management), secoiridoids (flavor determinants), as well as ginkgolides, cardenolides, and sesquiterpene lactones with pharmaceutical potential. Here, we provide a comprehensive overview of the underlying mechanisms.