Brassica villosa, a system for studying non-glandular trichomes and genes in the Brassicas

Perspectives for integrated insect pest protection in oilseed rape breeding

In the past, breeding for incorporation of insect pest resistance or tolerance into cultivars for use in integrated pest management schemes in oilseed rape/canola (Brassica napus) production has hardly ever been approached. This has been largely due to the broad availability of insecticides and the complexity of dealing with high-throughput phenotyping of insect performance and plant damage parameters. However, recent changes in the political framework in many countries demand future sustainable crop protection which makes breeding approaches for crop protection as a measure for pest insect control attractive again. At the same time, new camera-based tracking technologies, new knowledge-based genomic technologies and new scientific insights into the ecology of insect-Brassica interactions are becoming available. Here we discuss and prioritise promising breeding strategies and direct and indirect breeding targets, and their time-perspective for future realisation in integrated insect pest protection of oilseed rape. In conclusion, researchers and oilseed rape breeders can nowadays benefit from an array of new technologies which in combination will accelerate the development of improved oilseed rape cultivars with multiple insect pest resistances/tolerances in the near future.

Crop Wild Relatives (CWRs) Threatened and Endemic to Italy: Urgent Actions for Protection and Use

An updated overview of the 29 threatened crop wild relatives (CWRs) endemic to Italy is presented, namely: Arrhenatherum elatius subsp. nebrodense, Barbarea rupicola, Brassica baldensis, Brassica glabrescens, Brassica macrocarpa, Brassica rupestris subsp. hispida, Brassica rupestris subsp. rupestris, Brassica tardarae, Brassicatrichocarpa, Brassica tyrrhena, Brassica villosa subsp. bivonana, Brassica villosa subsp. brevisiliqua, Brassica villosa subsp. drepanensis, Brassica villosa subsp. tineoi, Brassica villosa subsp. villosa, Daucus broteroi, Daucus carota subsp. rupestris, Daucus nebrodensis, Diplotaxis scaposa, Festuca centroapenninica, Lathyrus apenninus, Lathyrus odoratus, Malus crescimannoi, Phalaris arundinacea subsp. rotgesii, Vicia brulloi, Vicia consentina, Vicia giacominiana, Vicia ochroleuca subsp. ochroleuca, Vicia tenuifolia subsp. elegans. Data concerning geographical distribution, ecology (including plant communities and habitats of the Directive 92/43/EEC), genetics (chromosome number, breeding system, and/or the existence of gene pools), threat status at the national and international level (Red Lists), key plant properties, and in situ and ex situ conservation were analyzed and shown. At present, most of the listed endemic CWRs, 23 out of 29, have no gene pool at all, so they are CWRs only according to the taxon group and not according to the gene pool concept. In addition, there is a serious lack of data on the ex situ conservation in gene banks, with 16 species identified as high priority (HP) while 22 taxa have high priority (A) for in situ conservation. With the aim of their protection, conservation, and valorization, specific and urgent actions are recommended.

Effect of gene mutation of plants on their mechano-sensibility: the mutant of EXO70H4 influences the buckling of Arabidopsis trichomes

With the development of molecular biology, more and more mutants of plants have been constructed, where gene mutants have been found to influence not only the biological processes but also biophysical behaviors of plant cells. Trichomes are an important appendage, which has been found to act as an active mechanosensory switch transducing mechanical signals into physiology changes, where the mechanical property of trichomes is vital for such functions. Up to now, over 40 different genes have been found with the function of regulating trichome cell morphogenesis; however, the effect of gene mutants on trichome mechanosensory function remains elusive. In this study, we found that EXO70H4, one of the most up-regulated genes in the mature trichome, not only affects the thickness of the trichome cell wall but also the mechanical property (i.e., the Young's modulus) of trichomes. Finite element method simulation results show that the buckling instability and stress concentration (e.g., exerted by insects) cannot occur on the base of the mutant exo70H4 trichome, which might further interrupt the mechanical signal transduction from branches to the base of trichomes. These results indicated that the mutant exo70H4 trichome might lack the ability to act as an active mechanosensory switch against chewing insect herbivores. Our findings provide new information about the effect of gene mutation (like crop mutants) on the mechano-sensibility and capability to resist the agricultural pests or lodging, which could be of great significance to the development of agriculture.

The Molecular Basis of Kale Domestication: Transcriptional Profiling of Developing Leaves Provides New Insights Into the Evolution of a Brassica oleracea Vegetative Morphotype

Morphotypes of Brassica oleracea are the result of a dynamic interaction between genes that regulate the transition between vegetative and reproductive stages and those that regulate leaf morphology and plant architecture. In kales, ornate leaves, extended vegetative phase, and nutritional quality are some of the characters potentially selected by humans during domestication. We used a combination of developmental studies and transcriptomics to understand the vegetative domestication syndrome of kale. To identify candidate genes that are responsible for the evolution of domestic kale, we searched for transcriptome-wide differences among three vegetative B. oleracea morphotypes. RNA-seq experiments were used to understand the global pattern of expressed genes during a mixture of stages at one time in kale, cabbage, and the rapid cycling kale line TO1000. We identified gene expression patterns that differ among morphotypes and estimate the contribution of morphotype-specific gene expression that sets kale apart (3958 differentially expressed genes). Differentially expressed genes that regulate the vegetative to reproductive transition were abundant in all morphotypes. Genes involved in leaf morphology, plant architecture, defense, and nutrition were differentially expressed in kale. This allowed us to identify a set of candidate genes we suggest may be important in the kale domestication syndrome. Understanding candidate genes responsible for kale domestication is of importance to ultimately improve Cole crop production.

An Effective Screening Method and a Reliable Screening Trait for Salt Tolerance of Brassica napus at the Germination Stage

Salinity is a major and complex abiotic stress that inhibits plant growth and reduces crop yield. Given the global increase in soil salinity, there is a need to develop salt-tolerant species. Brassica napus L. is an important oilseed crop with some level of salt tolerance. However, few studies have evaluated its salt tolerance thoroughly or screened for traits that can be reliably evaluated for salt tolerance. Here, we evaluated salt tolerance in 549 B. napus inbred lines with different genetic backgrounds using the membership function value (MFV) of certain traits, including the germination rate, root and shoot length, root and shoot fresh weight, and total fresh weight. According to the evaluation criteria-mean MFV, 50 highly salt-tolerant, 115 salt-tolerant, 71 moderately salt-tolerant, 202 salt-sensitive, and 111 highly salt-sensitive inbred lines were screened at the germination stage. We also developed a mathematical evaluation model and identified that the salt tolerance index of shoot fresh weight is a single trait that reliably represents the salt tolerance of B. napus germplasm at the germination stage. These results are useful for evaluating and breeding salt-tolerant B. napus germplasm.

The biochemical composition and transcriptome of cotyledons from Brassica napus lines expressing the AtGL3 transcription factor and exhibiting reduced flea beetle feeding

BACKGROUND

Previously, transgenic trichome-bearing (hairy leaf) Brassica napus lines expressing either the Arabidopsis thaliana GL3 gene (line AtGL3+) [1] or the AtGL3 gene in combination with an RNAi construct to down-regulate TTG1 (line K-5-8) [2] were developed. The leaves of these lines exhibited altered insect feeding (flea beetle) and oviposition (diamondback moth) behaviour compared to the non-transgenic semi-glabrous leaves of B. napus cv. Westar. Interestingly, the cotyledons of these lines remained glabrous, but also showed reduced feeding by flea beetles. Here we examine the composition and global transcriptome of the glabrous cotyledons from these transgenic lines to ascertain the mechanism(s) underlying this unexpected phenomenon.

RESULTS

Approximately, 7500 genes were up-regulated in cotyledons of each hairy line, compared with < 30 that were down-regulated. The up-regulated genes included those involved in cell wall synthesis, secondary metabolite production, redox, stress and hormone-related responses that have the potential to impact host plant cues required to elicit defense responses toward insect pests. In particular, the expression of glucosinolate biosynthetic and degradation genes were substantially altered in the glabrous cotyledons of the two hairy leaf lines. The transcriptomic data was supported by glucosinolate and cell wall composition profiles of the cotyledons. Changes in gene expression were much more extreme in the AtGL3+ line compared with the K-5-8 line in terms of diversity and intensity.

CONCLUSIONS

The study provides a roadmap for the isolation and identification of insect resistance compounds and proteins in the glabrous cotyledons of these hairy leaf lines. It also confirms the impact of mis-expression of GL3 and TTG1 on types of metabolism other than those associated with trichomes. Finally, the large number of up-regulated genes encoding heat shock proteins, PR proteins, protease inhibitors, glucosinolate synthesis/breakdown factors, abiotic stress factors, redox proteins, transcription factors, and proteins required for auxin metabolism also suggest that these cotyledons are now primed for resistance to other forms of biotic and abiotic stress.

Effects of Ca addition on the uptake, translocation, and distribution of Cd in Arabidopsis thaliana

Cadmium (Cd) pollution poses a risk to human health for its accumulation in soil and crops, but this can be alleviated by calcium (Ca) addition. However, its mechanism remains unclear yet. In this study, Arabidopsis thaliana was used to explore the alleviating effects of Ca on Cd toxicity and its specific function during uptake, upward-translocation, and distribution of Cd. Supplementing plants with 5mM CaCl₂ alleviated the intoxication symptoms caused by 50μM CdCl₂, such as smaller leaves, early bolting and root browning. Ca addition decreased uptake of Cd, possibly by reducing the physical adsorption of Cd since the root cell membrane was well maintained and lignin deposition was decreased as well, and by decreasing symplastic Cd transport. Expression of the genes involved (AtZIP2 and AtZIP4) was also decreased. In addition, Ca accumulated in the plant shoot to help facilitating the upward-translocation of Cd, with evidence of higher translocation factor and expression of genes that were involved in Ca transport (AtPCR1) and Cd xylem loading (AtHMA2 and AtHMA4). Dithizone-staining of Cd in leaves showed that in Cd+Ca-treated plants, Ca addition initially protected the leaf stomata by preventing Cd from entering guard cells, but with prolonged Cd treatment facilitated the Cd accumulation around trichomes and maybe its excretion. We conclude that Ca promotes the upward-translocation of Cd and changes its distribution in leaves. The results may have relevance for bioremediation.

Gradient Mechanical Properties Facilitate Arabidopsis Trichome as Mechanosensor

It has been reported that Arabidopsis thaliana leaf trichome can act as a mechanosensory switch, transducing mechanical stimuli into physiological signals, mainly through a buckling instability to focus external force (e.g., exerted by insects) on the base of trichome. The material and structural properties of trichomes remain largely unknown in this buckling instability. In this report, we mainly focused on material standpoint to explore the possible mechanism facilitating the buckling instability. We observed that the Young's modulus of trichome cell wall decreased gradually from branch to the base region of trichome. Interestingly, we also found a corresponding decline of calcium concentration on the trichome cell wall. Results of finite element method (FEM) simulation suggested that such a gradient distribution of Young's modulus significantly promotes force focusing and buckling instability on the base of trichome. It is indicated that Arabidopsis trichome has developed into an active mechanosensor benefiting from gradient cell wall mechanical properties.

Cannabis sativa: The Plant of the Thousand and One Molecules

Cannabis sativa L. is an important herbaceous species originating from Central Asia, which has been used in folk medicine and as a source of textile fiber since the dawn of times. This fast-growing plant has recently seen a resurgence of interest because of its multi-purpose applications: it is indeed a treasure trove of phytochemicals and a rich source of both cellulosic and woody fibers. Equally highly interested in this plant are the pharmaceutical and construction sectors, since its metabolites show potent bioactivities on human health and its outer and inner stem tissues can be used to make bioplastics and concrete-like material, respectively. In this review, the rich spectrum of hemp phytochemicals is discussed by putting a special emphasis on molecules of industrial interest, including cannabinoids, terpenes and phenolic compounds, and their biosynthetic routes. Cannabinoids represent the most studied group of compounds, mainly due to their wide range of pharmaceutical effects in humans, including psychotropic activities. The therapeutic and commercial interests of some terpenes and phenolic compounds, and in particular stilbenoids and lignans, are also highlighted in view of the most recent literature data. Biotechnological avenues to enhance the production and bioactivity of hemp secondary metabolites are proposed by discussing the power of plant genetic engineering and tissue culture. In particular two systems are reviewed, i.e., cell suspension and hairy root cultures. Additionally, an entire section is devoted to hemp trichomes, in the light of their importance as phytochemical factories. Ultimately, prospects on the benefits linked to the use of the -omics technologies, such as metabolomics and transcriptomics to speed up the identification and the large-scale production of lead agents from bioengineered Cannabis cell culture, are presented.

Hairy Canola (Brasssica napus) re-visited: Down-regulating TTG1 in an AtGL3-enhanced hairy leaf background improves growth, leaf trichome coverage, and metabolite gene expression diversity

BACKGROUND

Through evolution, some plants have developed natural resistance to insects by having hairs (trichomes) on leaves and other tissues. The hairy trait has been neglected in Brassica breeding programs, which mainly focus on disease resistance, yield, and overall crop productivity. In Arabidopsis, a network of three classes of proteins consisting of TTG1 (a WD40 repeat protein), GL3 (a bHLH factor) and GL1 (a MYB transcription factor), activates trichome initiation and patterning. Introduction of a trichome regulatory gene AtGL3 from Arabidopsis into semi-glabrous Brassica napus resulted in hairy canola plants which showed tolerance to flea beetles and diamondback moths; however plant growth was negatively affected. In addition, the role of BnTTG1 transcription in the new germplasm was not understood.

RESULTS

Here, we show that two ultra-hairy lines (K-5-8 and K-6-3) with BnTTG1 knock-down in the hairy AtGL3+ B. napus background showed stable enhancement of trichome coverage, density, and length and restored wild type growth similar to growth of the semi-glabrous Westar plant. In contrast, over-expression of BnTTG1 in the hairy AtGL3+ B. napus background gave consistently glabrous plants of very low fertility and poor stability, with only one glabrous plant (O-3-7) surviving to the T3 generation. Q-PCR trichome gene expression data in leaf samples combining several leaf stages for these lines suggested that BnGL2 controlled B. napus trichome length and out-growth and that strong BnTTG1 transcription together with strong GL3 expression inhibited this process. Weak expression of BnTRY in both glabrous and trichome-bearing leaves of B. napus in the latter Q-PCR experiment suggested that TRY may have functions other than as an inhibitor of trichome initiation in the Brassicas. A role for BnTTG1 in the lateral inhibition of trichome formation in neighbouring cells was also proposed for B. napus. RNA sequencing of first leaves identified a much larger array of genes with altered expression patterns in the K-5-8 line compared to the hairy AtGL3(+) B. napus background (relative to the Westar control plant). These genes particularly included transcription factors, protein degradation and modification genes, but also included pathways that coded for anthocyanins, flavonols, terpenes, glucosinolates, alkaloids, shikimates, cell wall biosynthesis, and hormones. A 2nd Q-PCR experiment was conducted on redox, cell wall carbohydrate, lignin, and trichome genes using young first leaves, including T4 O-3-7-5 plants that had partially reverted to yield two linked growth and trichome phenotypes. Most of the trichome genes tested showed to be consistant with leaf trichome phenotypes and with RNA sequencing data in three of the lines. Two redox genes showed highest overall expression in K-5-8 leaves and lowest in O-3-7-5 leaves, while one redox gene and three cell wall genes were consistently higher in the two less robust lines compared with the two robust lines.

CONCLUSION

The data support the strong impact of BnTTG1 knockdown (in the presence of strong AtGL3 expression) at restoring growth, enhancing trichome coverage and length, and enhancing expression and diversity of growth, metabolic, and anti-oxidant genes important for stress tolerance and plant health in B. napus. Our data also suggests that the combination of strong (up-regulated) BnTTG1 expression in concert with strong AtGL3 expression is unstable and lethal to the plant.