Genetic and molecular analysis of trichome development in Arabis alpina

Locally Specific Genome-Wide Signatures of Adaptation to Environmental Variation at High Resolution in an Alpine Plant

Microevolutionary processes shape adaptive responses to heterogeneous environments, where these effects vary both among and within species. However, it remains largely unknown to which degree signatures of adaptation to environmental drivers can be detected based on the choice of spatial scale and genomic marker. We studied signatures of local adaptation across two levels of spatial extents, investigating complementary types of genomic variants-single-nucleotide polymorphisms (SNPs) and polymorphic transposable elements (TEs)-in populations of the alpine model plant species Arabis alpina . We coupled environmental factors, derived from remote sensed digital elevation models (DEMs) at very high resolution (0.5 m), with whole-genome sequencing data of 304 individuals across four populations. By comparing putatively adaptive loci detected between each local population versus a regional assessment including all populations simultaneously, we demonstrate that responses of A. alpina to similar amounts of abiotic variation are largely governed by local evolutionary processes. Furthermore, we find minimally overlapping signatures of local adaptation between SNPs and polymorphic TEs. Notably, functional annotations of candidate genes for adaptation revealed several symbiosis-related genes associated with the abiotic factors studied, which could represent selective pressures from biotic agents. Our results highlight the importance of considering different spatial extents and types of genomic polymorphisms when searching for signatures of adaptation to environmental variation. Such insights provide key information on microevolutionary processes and could guide management decisions to mitigate negative impacts of climate change on alpine plant populations.

Ice age-driven range shifts of diploids and expanding autotetraploids of Biscutella laevigata within a conserved niche

Early studies of the textbook mixed-ploidy system Biscutella laevigata highlighted diploids restricted to never-glaciated lowlands and tetraploids at high elevations across the European Alps, promoting the hypothesis that whole-genome duplication (WGD) is advantageous under environmental changes. Here we addressed long-held hypotheses on the role of hybridisation at the origin of the tetraploids, their single vs multiple origins, and whether a shift in climatic niche accompanied WGD. Climatic niche modelling together with spatial genetics and coalescent modelling based on ddRAD-seq genotyping of 17 diploid and 19 tetraploid populations was used to revisit the evolution of this species complex in space and time. Diploids differentiated into four genetic lineages corresponding to allopatric glacial refugia at the onset of the last ice age, whereas tetraploids displaying tetrasomic inheritance formed a uniform group that originated from southern diploids before the last glacial maximum. Derived from diploids occurring at high elevation, autotetraploids likely inherited their adaptation to high elevation rather than having evolved it through or after WGD. They further presented considerable postglacial expansion across the Alps and underwent admixture with diploids. Although the underpinnings of the successful expansion of autotetraploids remain elusive, differentiation in B. laevigata was chiefly driven by the glacial history of the Alps.

Genetic dissection of stem and leaf rachis prickles in diploid rose using a pedigree-based QTL analysis

Introduction

Prickles are often deemed undesirable traits in many crops, including roses (Rosa sp.), and there is demand for rose cultivars with no or very few prickles. This study aims to identify new and/or validate reported quantitative trait loci (QTLs) associated with stem and leaf rachis prickle density, characterize the effects of functional haplotypes for major QTLs, and identify the sources of QTL-alleles associated with increased/decreased prickle density in roses.

Methods

QTL mapping using pedigree-based analysis (PBA), and haplotype analysis were conducted on two multi-parental diploid rose populations (TX2WOB and TX2WSE).

Results and discussion

Twelve QTLs were identified on linkage groups (LGs) 2, 3, 4, and 6. The major QTLs for the stem prickle density were located between 42.25 and 45.66 Mbp on chromosome 3 of the Rosa chinensis genome assembly, with individual QTLs explaining 18 to 49% of phenotypic variance (PVE). The remaining mapped QTLs were minor. As for the rachis prickle density, several QTLs were detected on LG3, 4, and 6 with PVE 8 to 17%. Also, this study identified that ancestors R. wichurana 'Basye's Thornless', 'Old Blush', and the pollen parent of M4-4 were common sources of favorable alleles (q) associated with decreased prickle density, whereas 'Little Chief' and 'Srche Europy' were the source of unfavorable alleles (Q) in the TX2WOB and TX2WSE populations, respectively. The outcomes of this work complement other studies to locate factors that affect prickle density. These results can also be utilized to develop high-throughput DNA tests and apply parental selection to develop prickle-free rose cultivars.

Defects in Glabrous 3 (GL3) functionality underlie the absence of trichomes in Brassica napus

Previously, expression of the Arabidopsis thaliana GLABRA3 (GL3) induced trichome formation in Brassica napus. GL3 orthologues were examined from glabrous (B. oleracea), semi-glabrous (B. napus), moderately hirsute (B. rapa), and very hirsute (B. villosa) Brassica species. Ectopic expression of BnGL3, BrGL3 alleles, or BvGL3 induced trichome formation in glabrous B. napus with the effect on trichome number commensurate with density in the original accessions. Chimeric GL3 proteins in which the B. napus amino terminal region, which interacts with MYB proteins, or the middle region, which interacts with the WD40 protein TTG1, was exchanged with corresponding regions from A. thaliana were as stimulatory to trichome production as AtGL3. Exchange of the carboxy-terminal region containing a bHLH domain and an ACT domain did not alter the trichome stimulatory activity, although modeling of the ACT domain identified differences that could affect GL3 dimerization. B. napus A- and C-genomes orthologues differed in their abilities to form homo- and heterodimers. Modeling of the amino-terminal region revealed a conserved domain that may represent the MYB factor binding pocket. This region interacted with the MYB factors GL1, CPC, and TRY, as well as with JAZ8, which is involved in jasmonic acid-mediated regulation of MYC-like transcription factors. Protein interaction studies indicated that GL1 interaction with GL3 from B. napus and A. thaliana may underlie the difference in their respective abilities to induce trichome formation.

Quantitative analysis of MBW complex formation in the context of trichome patterning

Trichome patterning in Arabidopsis is regulated by R2R3MYB, bHLH and WDR (MBW) genes. These are considered to form a trimeric MBW protein complex that promotes trichome formation. The MBW proteins are engaged in a regulatory network to select trichome cells among epidermal cells through R3MYB proteins that can move between cells and repress the MBW complex by competitive binding with the R2R3MYB to the bHLHL protein. We use quantitative pull-down assays to determine the relative dissociation constants for the protein-protein interactions of the involved genes. We find similar binding strength between the trichome promoting genes and weaker binding of the R3MYB inhibitors. We used the dissociation constants to calculate the relative percentage of all possible complex combinations and found surprisingly low fractions of those complexes that are typically considered to be relevant for the regulation events. Finally, we predict an increased robustness in patterning as a consequence of higher ordered complexes mediated by GL3 dimerization.

Morphological and genetic evidence suggest gene flow among native and naturalized mint species

PREMISE

Cultivation and naturalization of plants beyond their natural range can bring previously geographically isolated taxa together, increasing the opportunity for hybridization, the outcomes of which are not predictable. Here, we explored the phenotypic and genomic effects of interspecific gene flow following the widespread cultivation of Mentha spicata (spearmint), M. longifolia, and M. suaveolens.

METHODS

We morphologically evaluated 155 herbarium specimens of three Mentha species and sequenced the genomes of a subset of 93 specimens. We analyzed the whole genomes in a population and the phylogenetic framework and associated genomic classifications in conjunction with the morphological assessments.

RESULTS

The allopolyploid M. spicata, which likely evolved in cultivation, had altered trichome characters, that is possibly a product of human selection for a more palatable plant or a byproduct of selection for essential oils. There were signs of genetic admixture between mints, including allopolyploids, indicating that the reproductive barriers between Mentha species with differences in ploidy are likely incomplete. Still, despite gene flow between species, we found that genetic variants associated with the cultivated trichome morphology continue to segregate.

CONCLUSIONS

Although hybridization, allopolyploidization, and human selection during cultivation can increase species richness (e.g., by forming hybrid taxa), we showed that unless reproductive barriers are strong, these processes can also result in mixing of genes between species and the potential loss of natural biodiversity.

Insights into salicylic acid-mediated redox homeostasis, carbohydrate metabolism and secondary metabolite involvement in improvement of photosynthetic performance, enzyme activities, ionomics, and yield in different varieties of Abelmoschus esculentus

Salicylic acid (SA) is a well-known signaling molecule and phenolic plant hormone. However, the optimal concentration of SA required for beneficial effects may vary across different plant species. The objective of this study was to investigate the effects of salicylic acid (SA) on two different varieties of Abelmoschus esculentus (Sakata-713 and Neelam) in order to determine the optimal concentration of SA and its impact on the growth, physiology, and biochemical processes of the plants. We conducted an experiment applying different SA concentrations (0, 10-4, 10-5, 10-6, 10-7 M) at 25 days after sowing (DAS) and evaluated various plant parameters at different stages. To evaluate various parameters sampling was performed at 30 and 45 DAS; yield traits were calculated at 60 DAS. The results indicate that SA application increased cell division, trichome number, chlorophyll content, photosynthesis, gas exchange traits, and elemental status which further boosted plants growth and yield traits. SA application stimulated activity of several enzymes that participate in carboxylation/decarboxylation homeostasis (carbonic anhydrase), nitrogen metabolism (nitrate reductase), Calvin cycle (Rubisco), TCA cycle (succinate dehydrogenase and fumarase) and secondary metabolism (phenylalanine lyase). A gradual increase in the production of secondary metabolites (total phenol, total flavonoid, anthocyanin) and carbon metabolism (total reducing sugars, starch, glucose, fructose, sucrose) was observed. Notably, SA treatment also played a vital role in maintaining a balanced equilibrium between reactive oxygen species (ROS) and the scavenging system (catalase, peroxidase, superoxide dismutase). Based on our results, the optimal concentration of SA was determined to be 10-5 M, as it yielded the most favourable outcomes among the different concentrations tested. Moreover, when comparing the two varieties of okra, Sakata-713 exhibited a more promising response to SA treatment compared to Neelam.

A conserved gene regulatory network controls root epidermal cell patterning in superrosid species

In superrosid species, root epidermal cells differentiate into root hair cells and nonhair cells. In some superrosids, the root hair cells and nonhair cells are distributed randomly (Type I pattern), and in others, they are arranged in a position-dependent manner (Type III pattern). The model plant Arabidopsis (Arabidopsis thaliana) adopts the Type III pattern, and the gene regulatory network (GRN) that controls this pattern has been defined. However, it is unclear whether the Type III pattern in other species is controlled by a similar GRN as in Arabidopsis, and it is not known how the different patterns evolved. In this study, we analyzed superrosid species Rhodiola rosea, Boehmeria nivea, and Cucumis sativus for their root epidermal cell patterns. Combining phylogenetics, transcriptomics, and cross-species complementation, we analyzed homologs of the Arabidopsis patterning genes from these species. We identified R. rosea and B. nivea as Type III species and C. sativus as Type I species. We discovered substantial similarities in structure, expression, and function of Arabidopsis patterning gene homologs in R. rosea and B. nivea, and major changes in C. sativus. We propose that in superrosids, diverse Type III species inherited the patterning GRN from a common ancestor, whereas Type I species arose by mutations in multiple lineages.

Regulation of capsule spine formation in castor

Castor (Ricinus communis L.) is a dicotyledonous oilseed crop that can have either spineless or spiny capsules. Spines are protuberant structures that differ from thorns or prickles. The developmental regulatory mechanisms governing spine formation in castor or other plants have remained largely unknown. Herein, using map-based cloning in 2 independent F2 populations, F2-LYY5/DL01 and F2-LYY9/DL01, we identified the RcMYB106 (myb domain protein 106) transcription factor as a key regulator of capsule spine development in castor. Haplotype analyses demonstrated that either a 4,353-bp deletion in the promoter or a single nucleotide polymorphism leading to a premature stop codon in the RcMYB106 gene could cause the spineless capsule phenotype in castor. Results of our experiments indicated that RcMYB106 might target the downstream gene RcWIN1 (WAX INDUCER1), which encodes an ethylene response factor known to be involved in trichome formation in Arabidopsis (Arabidopsis thaliana) to control capsule spine development in castor. This hypothesis, however, remains to be further tested. Nevertheless, our study reveals a potential molecular regulatory mechanism underlying the spine capsule trait in a nonmodel plant species.

Genome-Wide Investigation and Functional Analysis Reveal That CsGeBP4 Is Required for Tea Plant Trichome Formation

Tea plant trichomes not only contribute to the unique flavor and high quality of tea products but also provide physical and biochemical defenses for tea plants. Transcription factors play crucial roles in regulating plant trichome formation. However, limited information about the regulatory mechanism of transcription factors underlying tea plant trichome formation is available. Here, the investigation of trichome phenotypes among 108 cultivars of Yunwu Tribute Tea, integrated with a transcriptomics analysis of both hairy and hairless cultivars, revealed the potential involvement of CsGeBPs in tea trichome formation. In total, six CsGeBPs were identified from the tea plant genome, and their phylogenetic relationships, as well as the structural features of the genes and proteins, were analyzed to further understand their biological functions. The expression analysis of CsGeBPs in different tissues and in response to environmental stresses indicated their potential roles in regulating tea plant development and defense. Moreover, the expression level of CsGeBP4 was closely associated with a high-density trichome phenotype. The silencing of CsGeBP4 via the newly developed virus-induced gene silencing strategy in tea plants inhibited trichome formation, indicating that CsGeBP4 was required for this process. Our results shed light on the molecular regulatory mechanisms of tea trichome formation and provide new candidate target genes for further research. This should lead to an improvement in tea flavor and quality and help in breeding stress-tolerant tea plant cultivars.

Comparative expression analysis in three Brassicaceae species revealed compensatory changes of the underlying gene regulatory network

Trichomes are regularly distributed on the leaves of Arabidopsis thaliana. The gene regulatory network underlying trichome patterning involves more than 15 genes. However, it is possible to explain patterning with only five components. This raises the questions about the function of the additional components and the identification of the core network. In this study, we compare the relative expression of all patterning genes in A. thaliana, A. alpina and C. hirsuta by qPCR analysis and use mathematical modelling to determine the relative importance of patterning genes. As the involved proteins exhibit evolutionary conserved differential complex formation, we reasoned that the genes belonging to the core network should exhibit similar expression ratios in different species. However, we find several striking differences of the relative expression levels. Our analysis of how the network can cope with such differences revealed relevant parameters that we use to predict the relevant molecular adaptations in the three species.

Combined morphological and multi-omics analyses to reveal the developmental mechanism of Zanthoxylum bungeanum prickles

Zanthoxylum bungeanum Maxim. as an important economic forest, its epidermis bears prickles which complicate the harvesting process and increase the labor costs. To explore the developmental mechanism of prickles, three varieties of Zanthoxylum bungeanum (PZB, SZB, GSZB) were selected for morphological and multi-omics analyses. The absorption spectra of prickles and stems were detected using Fourier-transform infrared spectroscopy (FTIR), and they were found different at 1617, 1110, 3319, and 1999 cm^-1. The morphology of prickles and stems were observed using light microscopy and transmission electron microscopy (TEM). The growth direction of cells on the prickle side and stem side were perpendicular to each other, and there was a resembling abscission zone (RAZ) between them. The vacuolar deposits of prickle cells were much more than stem cells, indicating that the lignification degree of prickles was higher than stems. In addition, 9 candidate genes (ZbYABBY2, ZbYABBY1, ZbYABBY5, ZbWRKY, ZbLOG5, ZbAZG2, ZbGh16, ZbIAA33, and ZbGh16X1) were screened out and validated base on transcriptome and qRT-PCA. As well as, 30 key metabolites were found related to prickle development base on metabolome analysis. Among them, 4-hydroxy-2-oxopentanoate, trans-2-hydroxy-cinnamate, trans-cinnamate, polyhydroxy-fatty acid, 10,16-dihydroxypalmitate, cinnamic acid were related to the biosynthesis of cutin, suberine and wax. Indole-3-acetate, tryptamine, anthranilate, fromylanthranilate, N6-(delta2-isopentenyl)-adenine were related to plant hormone signal transduction. Generally, this is the first study to reveal the developmental mechanism of prickles. The results of this study lay the foundation for the breeding of non-prickle Zanthoxylum bungeanum.

The genome of the recretohalophyte Limonium bicolor provides insights into salt gland development and salinity adaptation during terrestrial evolution

Halophytes have evolved specialized strategies to cope with high salinity. The extreme halophyte sea lavender (Limonium bicolor) lacks trichomes but possesses salt glands on its epidermis that can excrete harmful ions, such as sodium, to avoid salt damage. Here, we report a high-quality, 2.92-Gb, chromosome-scale L. bicolor genome assembly based on a combination of Illumina short reads, single-molecule, real-time long reads, chromosome conformation capture (Hi-C) data, and Bionano genome maps, greatly enriching the genomic information on recretohalophytes with multicellular salt glands. Although the L. bicolor genome contains genes that show similarity to trichome fate genes from Arabidopsis thaliana, it lacks homologs of the decision fate genes GLABRA3, ENHANCER OF GLABRA3, GLABRA2, TRANSPARENT TESTA GLABRA2, and SIAMESE, providing a molecular explanation for the absence of trichomes in this species. We identified key genes (LbHLH and LbTTG1) controlling salt gland development among classical trichome homologous genes and confirmed their roles by showing that their mutations markedly disrupted salt gland initiation, salt secretion, and salt tolerance, thus offering genetic support for the long-standing hypothesis that salt glands and trichomes may share a common origin. In addition, a whole-genome duplication event occurred in the L. bicolor genome after its divergence from Tartary buckwheat and may have contributed to its adaptation to high salinity. The L. bicolor genome resource and genetic evidence reported in this study provide profound insights into plant salt tolerance mechanisms that may facilitate the engineering of salt-tolerant crops.

CsMYB1 integrates the regulation of trichome development and catechins biosynthesis in tea plant domestication

Tea trichomes synthesize numerous specialized metabolites to protect plants from environmental stresses and contribute to tea flavours, but little is known about the regulation of trichome development. Here, we showed that CsMYB1 is involved in the regulation of trichome formation and galloylated cis-catechins biosynthesis in tea plants. The variations in CsMYB1 expression levels are closely correlated with trichome indexes and galloylated cis-catechins contents in tea plant populations. Genome resequencing showed that CsMYB1 may be selected in modern tea cultivars, since a 192-bp insertion in CsMYB1 promoter was found exclusively in modern tea cultivars but not in the glabrous wild tea Camellia taliensis. Several enhancers in the 192-bp insertion increased CsMYB1 transcription in modern tea cultivars that coincided with their higher galloylated cis-catechins contents and trichome indexes. Biochemical analyses and transgenic data showed that CsMYB1 interacted with CsGL3 and CsWD40 and formed a MYB-bHLH-WD40 (MBW) transcriptional complex to activate the trichome regulator genes CsGL2 and CsCPC, and the galloylated cis-catechins biosynthesis genes anthocyanidin reductase and serine carboxypeptidase-like 1A. CsMYB1 integratively regulated trichome formation and galloylated cis-catechins biosynthesis. Results suggest that CsMYB1, trichome and galloylated cis-catechins are coincidently selected during tea domestication by harsh environments for improved adaption and by breeders for better tea flavours.

Rose without prickle: genomic insights linked to moisture adaptation

Prickles act against herbivores, pathogens or mechanical injury, while also preventing water loss. However, whether prickles have new function and the molecular genetics of prickle patterning remain poorly explored. Here, we generated a high-quality reference genome assembly for ‘Basye's Thornless’ (BT), a prickle-free cultivar of Rosa wichuraiana, to identify genetic elements related to stem prickle development. The BT genome harbors a high level of sequence diversity in itself and with cultivar ‘Old Blush’ (R. chinensis), a founder genotype in rose domestication. Inheritance of stem prickle density was determined and two QTL were identified. Differentially expressed genes in QTL were involved in water-related functions, suggesting that prickle density may hitchhike with adaptations to moist environments. While the prickle-related gene-regulatory-network (GRN) was highly conserved, the expression variation of key candidate genes was associated with prickle density. Our study provides fundamental resources and insights for genome evolution in the Rosaceae. Ongoing efforts on identification of the molecular bases for key rose traits may lead to improvements for horticultural markets.

Rambutan genome revealed gene networks for spine formation and aril development

Rambutan is a popular tropical fruit known for its exotic appearance, has long flexible spines on shells, extraordinary aril growth, desirable nutrition, and a favorable taste. The genome of an elite rambutan cultivar Baoyan 7 was assembled into 328 Mb in 16 pseudo-chromosomes. Comparative genomics analysis between rambutan and lychee revealed that rambutan chromosomes 8 and 12 are collinear with lychee chromosome 1, which resulted in a chromosome fission event in rambutan (n = 16) or a fusion event in lychee (n = 15) after their divergence from a common ancestor 15.7 million years ago. Root development genes played a crucial role in spine development, such as endoplasmic reticulum pathway genes, jasmonic acid response genes, vascular bundle development genes, and K⁺ transport genes. Aril development was regulated by D-class genes (STK and SHP1), plant hormone and phenylpropanoid biosynthesis genes, and sugar metabolism genes. The lower rate of male sterility of hermaphroditic flowers appears to be regulated by MYB24. Population genomic analyses revealed genes in selective sweeps during domestication that are related to fruit morphology and environment stress response. These findings enhance our understanding of spine and aril development and provide genomic resources for rambutan improvement.

Genetic and Molecular Analysis of Root Hair Development in Arabis alpina

Root hair formation in Arabidopsis thaliana is a well-established model system for epidermal patterning and morphogenesis in plants. Over the last decades, many underlying regulatory genes and well-established networks have been identified by thorough genetic and molecular analysis. In this study, we used a forward genetic approach to identify genes involved in root hair development in Arabis alpina, a related crucifer species that diverged from A. thaliana approximately 26-40 million years ago. We found all root hair mutant classes known in A. thaliana and identified orthologous regulatory genes by whole-genome or candidate gene sequencing. Our findings indicate that the gene-phenotype relationships regulating root hair development are largely conserved between A. thaliana and A. alpina. Concordantly, a detailed analysis of one mutant with multiple hairs originating from one cell suggested that a mutation in the SUPERCENTIPEDE1 (SCN1) gene is causal for the phenotype and that AaSCN1 is fully functional in A. thaliana. Interestingly, we also found differences in the regulation of root hair differentiation and morphogenesis between the species, and a subset of root hair mutants could not be explained by mutations in orthologs of known genes from A. thaliana. This analysis provides insight into the conservation and divergence of root hair regulation in the Brassicaceae.

Arabis alpina: A perennial model plant for ecological genomics and life-history evolution

Many model organisms were chosen and achieved prominence because of an advantageous combination of their life‐history characteristics, genetic properties and also practical considerations. Discoveries made in Arabidopsis thaliana, the most renowned noncrop plant model species, have markedly stimulated studies in other species with different biology. Within the family Brassicaceae, the arctic–alpine Arabis alpina has become a model complementary to Arabidopsis thaliana to study the evolution of life‐history traits, such as perenniality, and ecological genomics in harsh environments. In this review, we provide an overview of the properties that facilitated the rapid emergence of A. alpina as a plant model. We summarize the evolutionary history of A. alpina, including genomic aspects, the diversification of its mating system and demographic properties, and we discuss recent progress in the molecular dissection of developmental traits that are related to its perennial life history and environmental adaptation. From this published knowledge, we derive open questions that might inspire future research in A. alpina, other Brassicaceae species or more distantly related plant families.

Genetic determinism of prickles in rose

KEY MESSAGE

The genetic determinism of prickle in rose is complex, with a major locus on LG3 that controls the absence/presence of prickles on the rose stem. Rose is one of the major ornamental plants. The selection of glabrous cultivars is an important breeding target but remains a difficult task due to our limited genetic knowledge. Our objective was to understand the genetic and molecular determinism of prickles. Using a segregating diploid rose F1 population, we detected two types of prickles (glandular and non-glandular) in the progeny. We scored the number of non-glandular prickles on the floral and main stems for three years. We performed QTL analysis and detected four prickle loci on LG1, 3, 4 and 6. We determined the credible interval on the reference genome. The QTL on LG3 is a major locus that controls the presence of prickles, and three QTLs (LG3, 4 and 1) may be responsible for prickle density. We further revealed that glabrous hybrids are caused by the combination of the two recessive alleles from both parents. In order to test whether rose prickles could originate from a 'trichome-like structure,' we used a candidate approach to characterize rose gene homologues known in Arabidopsis, involved in trichome initiation. Four of these homologues were located within the overlapping credible interval of the detected QTLs. Transcript accumulation analysis weakly supports the involvement of trichome homologous genes, in the molecular control of prickle initiation. Our studies provide strong evidence for a complex genetic determinism of stem prickle and could help to establish guidelines for glabrous rose breeding. New insights into the relationship between prickles and trichomes constitute valuable information for reverse genetic research on prickles.

Glandular trichomes: micro-organs with model status?

Glandular trichomes are epidermal outgrowths that are the site of biosynthesis and storage of large quantities of specialized metabolites. Besides their role in the protection of plants against biotic and abiotic stresses, they have attracted interest owing to the importance of the compounds they produce for human use; for example, as pharmaceuticals, flavor and fragrance ingredients, or pesticides. Here, we review what novel concepts investigations on glandular trichomes have brought to the field of specialized metabolism, particularly with respect to chemical and enzymatic diversity. Furthermore, the next challenges in the field are understanding the metabolic network underlying the high productivity of glandular trichomes and the transport and storage of metabolites. Another emerging area is the development of glandular trichomes. Studies in some model species, essentially tomato, tobacco, and Artemisia, are now providing the first molecular clues, but many open questions remain: How is the distribution and density of different trichome types on the leaf surface controlled? When is the decision for an epidermal cell to differentiate into one type of trichome or another taken? Recent advances in gene editing make it now possible to address these questions and promise exciting discoveries in the near future.

Evolutionary Comparison of the Developmental/Physiological Phenotype and the Molecular Behavior of SPIRRIG Between Arabidopsis thaliana and Arabis alpina

Beige and Chediak Higashi (BEACH) domain proteins mediate membrane-dependent processes in eukaryotic cells. The plant BEACH domain protein SPIRRIG in A. thaliana (AtSPI) was shown to display a similar molecular behavior as its yeast and animal homologs, along with a range of cell morphological defects. In addition, AtSPI was shown to interact with the P-body component DCP1, to differentially effect RNA levels and to be involved in the regulation of RNA stability in the context of salt stress responses. To determine, whether the dual function of SPI in apparently unrelated molecular pathways and traits is evolutionary conserved, we analyzed three Aaspi alleles in Arabis alpina. We show that the molecular behavior of the SPI protein and the role in cell morphogenesis and salt stress response are similar in the two species, though we observed distinct deviations in the phenotypic spectrum.