Exploiting the wild crucifer <Emphasis Type="Italic">Thlaspi arvense</Emphasis> to identify conserved and novel genes expressed during a plant’s response to cold stress

Thlaspi arvense, a wild species from the Brassicaceae family, was shown to have a higher level of freezing tolerance than either of its close relatives, the model plant Arabidopsis thaliana or the crop Brassica napus (canola). Over 600 clones were sequenced from a subtractive cDNA library generated from cold treated T. arvense tissue, establishing that T. arvense shared significant sequence identity with both A. thaliana and B. napus (90–92%). In light of the strong sequence similarity between T. arvense and A. thaliana and to exploit the available genomics resources for Arabidopsis, the efficacy of using long 70 mer oligonucleotide whole genome Arabidopsis microarrays was tested for T. arvense. Gene expression in T. arvense leaf tissue during the very early stages of cold acclimation (or cold stress) was assayed at three time points and compared to an untreated control. This analysis highlights some of the difficulties and benefits of using cross-species microarray analysis. The data suggested that T. arvense responds in a similar fashion to cold stress as the model plant A. thaliana. However, for a number of genes quantitative differences in the level and timing of expression were identified. One of the most notable differences suggested that sulphur assimilation leading to the increased production of the methyl donor S-adenosyl-methionine was playing a role in the response of T. arvense to cold stress. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

TcYSL3, a member of the YSL gene family from the hyper-accumulator Thlaspi caerulescens, encodes a nicotianamine-Ni/Fe transporter

The two main features of plant hyper-accumulator species are the massive translocation of heavy metal ions to the aerial parts and their tolerance to such high metal concentrations. Recently, several lines of evidence have indicated a role for nicotianamine (NA) in metal homeostasis, through the chelation and transport of NA-metal complexes. The function of transport of NA-metal chelates, required for the loading and unloading of vessels, has been assigned to the Yellow Stripe 1 (YSL)-Like family of proteins. We have characterized three YSL genes in Thlaspi caerulescens in the context of hyper-accumulation. The three YSL genes are expressed at high rates compared with their Arabidopsis thaliana homologs but with distinct patterns. While TcYSL7 was highly expressed in the flowers, TcYSL5 was more highly expressed in the shoots, and the expression of TcYSL3 was equivalent in all the organs tested. In situ hybridizations have shown that TcYSL7 and TcYSL5 are expressed around the vasculature of the shoots and in the central cylinder in the roots. The exposure to heavy metals (Zn, Cd, Ni) does not affect the high and constitutive expression of the TcYSL genes. Finally, we have demonstrated by mutant yeast complementation and uptake measurements that TcYSL3 is an Fe/Ni-NA influx transporter. This work provides therefore molecular, histological and biochemical evidence supporting a role for YSL transporters in the overall scheme of NA and NA-metal, particularly NA-Ni, circulation in a metal hyper-accumulator plant.     

Zinc hyperaccumulation and cellular distribution in Arabidopsis halleri

Although Arabidopsis halleri ( = Cardaminopsis halleri) is known as a Zn hyperaccumulator, there have been no detailed studies on Zn accumulation, tolerance and cellular distribution in this species. In a hydroponic experiment, A. halleri grew healthily with Zn concentrations varying from 1 to 1000 μ M , without showing phytotoxicity or reduction in root or shoot dry weights. The concentration of Zn in the shoots increased from 300 μ g g ^{? 1} dry weight in the 1 μ M Zn treatment to 32 000 μ g g ^{? 1} in the 1000 μ M Zn treatment. Approximately 60% of the total Zn in the shoots were water‐soluble, and there was no evidence of Zn and P co‐precipitation. Both citric and malic acid concentrations in the shoots were not significantly affected by the Zn treatments, whereas in the roots there was a positive response in both organic acids to increasing Zn in solution. Cellular distribution of Zn, Ca and K in frozen hydrated leaf tissues was examined using energy‐dispersive X‐ray microanalysis. Zinc was sequestered in the base of trichomes, whereas the middle and upper parts of trichomes were highly enriched with Ca. Mesophyll cells appeared to have more Zn than the epidermis, probably because the latter were very small in size. Similarities and differences between A. halleri and the other well‐known Zn hyperaccumulator, Thlaspi caerulescens, are discussed.     

Within and between population variation for zinc and nickel accumulation in two species of Thlaspi (Brassicaceae)

In this study, the differences in zinc (Zn) and nickel (Ni) hyperaccumulation were investigated between three populations of Thlaspi pindicum together with genetic variation within populations of T. pindicum and Thlaspi alpinum var. sylvium, both serpentine endemics. Three experiments were conducted under standard conditions in hydroponic assay. Each experiment contained three treatments of metal: 100 microm Zn, 100 microm Ni, and combined 100/100 microm Zn/Ni. Genetic variation within populations was determined using maternal families. No genetic variation within populations was found for either Zn or Ni hyperaccumulation for both T. pindicum and T. alpinum var. sylvium, but differences were observed for both Zn and Ni hyperaccumulation between populations of T. pindicum. In combined Zn/Ni treatments, Zn inhibited Ni translocation in both species, which is unexpected considering that these species are serpentine endemics and well known Ni hyperaccumulators. The lack of genetic variation for metal hyperaccumulation is possibly due to inbreeding. Since Zn hyperaccumulation is not manifested in the field, inadvertent uptake of Zn is a plausible hypothesis for its preferential uptake.     

几种有机添加剂对遏蓝菜和东南景天吸收提取Zn的效应

通过盆栽试验,比较研究乙二胺四乙酸二钠盐(EDTA)、味精废液、柠檬酸、乙酸、草酸和混合试剂(柠檬酸∶味精废液∶EDTA∶KC l=10∶1∶2∶3)对Zn超累积植物遏蓝菜(T h lasp i caeru lescens)和东南景天(S edum a lf red ii)吸收提取Zn的影响。结果表明:各种添加剂均提高土壤中的水提取态和NH4NO3提取态Zn的含量,其顺序为EDTA混合试剂>味精废液>有机酸。除乙酸和味精废液外,其余添加剂都显著促进遏蓝菜的生长,以混合试剂的增产效果最好;但只有EDTA和混合试剂在浓度为10mm o l/kg土时提高了东南景天的生物量。混合试剂在浓度为6~10 mm o l/kg土时促进遏蓝菜对Zn的吸收和向地上部转移;EDTA和浓度为10mm o l/kg的混合试剂能显著促进东南景天对Zn的吸收和向地上部的转移。因此东南景天配合环境风险较小、用量为10mm o l/kg土的混合试剂较适合我国南方的Zn污染土壤。     

Heavy metal uptake and chemical changes in the rhizosphere of Thlaspi caerulescens and Thlaspi ochroleucum grown in contaminated soils

Thlaspi caerulescens (J. and C. Presl) and Thlaspi ochroleucum (Boiss. ex Heldr) were grown in three different soils containing moderate to high amounts of heavy metals in a pot experiment, using a rhizobag technique. T. caerulescens accumulated significantly more Zn in the shoots than T. ochroleucum. The concentrations of Zn in the shoots of T. caerulescens ranged from 3100 to 8100 mg kg^-1 dry matter (DM), but only from 800 to 1600 mg kg^-1 DM in T. ochroleucum. Total uptake of Zn in the shoots of T. caerulescens was about 5 times that of T. ochroleucum. In contrast, the differences between the two species in the uptake of Cd, Cr, Cu, Ni and Pb were generally small. Concentrations of mobile Zn (extractable with 1M NH₄NO₃) in the rhizosphere and non-rhizosphere soils decreased considerably after growth of both plants, but the decreases were greater with T. caerulescens than with T. ochroleucum. The decreases in the mobile fraction accounted for less than 10% of the total Zn uptake by T. caerulescens indicating that this species was effective in mobilising Zn from less soluble fractions in the soils. The rhizosphere soils tended to have higher concentrations of mobile Zn than the non-rhizosphere soils, probably because of the lower pH in the rhizosphere. The pH in the rhizosphere soils was 0.2-0.4 units lower than that in the non-rhizosphere soils at the end of the experiment. However, there were no significant differences between the two species in the degree of rhizosphere acidification. The results suggest that T. caerulescens has potential for removing Zn from moderately to highly contaminated soils, but that this ability was not related to the pH changes in the rhizosphere.     

A draft genome of field pennycress (Thlaspi arvense) provides tools for the domestication of a new winter biofuel crop

Field pennycress (Thlaspi arvense L.) is being domesticated as a new winter cover crop and biofuel species for the Midwestern United States that can be double-cropped between corn and soybeans. A genome sequence will enable the use of new technologies to make improvements in pennycress. To generate a draft genome, a hybrid sequencing approach was used to generate 47 Gb of DNA sequencing reads from both the Illumina and PacBio platforms. These reads were used to assemble 6,768 genomic scaffolds. The draft genome was annotated using the MAKER pipeline, which identified 27,390 predicted protein-coding genes, with almost all of these predicted peptides having significant sequence similarity to Arabidopsis proteins. A comprehensive analysis of pennycress gene homologues involved in glucosinolate biosynthesis, metabolism, and transport pathways revealed high sequence conservation compared with other Brassicaceae species, and helps validate the assembly of the pennycress gene space in this draft genome. Additional comparative genomic analyses indicate that the knowledge gained from years of basic Brassicaceae research will serve as a powerful tool for identifying gene targets whose manipulation can be predicted to result in improvements for pennycress.