This study was performed to examine the accumulated concentrations (conc.) of cadmium (Cd) in the organs of Arabidopsis thaliana grown in the soil with different conc. of Cd. The official standard conc. of Cd of pollutant exhaust notified by the Korean ministry of environment (0.1 mg/L) and ten times higher (1 mg/L) and fifty times higher (5 mg/L) conc. and no Cd in the soil as control were used for this investigation. The results showed that accumulated conc. of Cd in the stems of plant grown in the soil with different conc. (0.1, 1 and 5 mg/L) were increased 9%, 24% and 286% respectively, compared with normal plant stem. The accumulated conc. of Cd in the leafs of plant grown in the soil with official standard conc. and conc. ten times higher and conc. fifty times higher were increased 3%, 22% and 453%, respectively, compared with normal plant leaf. The accumulated conc. of Cd in the root of plant grown in the soil with 0.1 and 1 mg/L conc. of Cd were increased 6%, 19%, respectively, compared with normal plant root. However, it was observed about 84% of increased accumulation of the Cd in the root of plant, when highest (5 mg/L) conc. was used. The accumulated conc. of Cd in the different organs of Arabidopsis thaliana were increased according to increase of Cd conc. in the soil. When official standard conc. and ten times higher conc. of Cd were used, the accumulated conc. of Cd increased average 6%, 21%, respectively, compared with normal plant organ, and the accumulated conc. of Cd between leaf, stem and root were not significant. However, the accumulated conc. of Cd in the plant organs grown in the conc. fifty times higher were increased about 285%, compared with normal plant. In addition, the accumulated conc. of Cd in different organs of Arabidopsis thaliana exhibited wide differences between organs, that is, stem was increased 118% than root, leaf was increased 256%, 64% than root and stem, respectively. These results show that accumulated conc. of Cd in Arabidopsis thaliana with highest (5 mg/L) conc. of Cd in soil, were much higher in the leaf than the stem or root in proportion to the conc. of Cd contaminated within the soil.

The MYB transcription factors play important roles in the regulation of many secondary metabolites at the transcriptional level. We evaluated the possible roles of the Arabidopsis R2R3-MYB transcription factor genes in flavonoid biosynthesis as they are induced by UV-B irradiation but are largely unexplored in terms of their associated phenotypes. We found that one member of this gene family, AtMYB60, inhibits anthocyanin biosynthesis in the lettuce plant. Wild type lettuce normally accumulates anthocyanin, predominantly cyanidin and traces of delphinidin, and develops a red pigmentation. However, the accumulation of anthocyanin pigments in AtMYB60 overexpressing lettuce was inhibited. We further found a complete absence of DFR transcripts in AtMYB60 overexpressing lettuce, whereas other biosynthetic genes in the anthocyanin metabolism pathway were expressed. To provide genetic tools the regulation of seed color of rapeseed which has been target for fuel, AtMYB was overexpressed in rapeseed. Transgenic plants showed lighter seed color and improved tolerance to abiotic stress than the wild type plants. The elucidation of the roles of the AtMYB60 transcription factor will facilitate further studies and provide genetic tools to better understand the regulation in plants of the genes controlled by the MYB-type transcription factors.

Organ abscission is a programmed cell separation process that results in the detachment of an entire organ from a plant. Our goal is to understand the signaling pathway that regulates this physiological process. The receptor-like protein kinase, HAESA (HAE), and its paralog, HAESA-like 2 (HSL2), are both expressed in the floral abscission zones in Arabidopsis thaliana. Loss-of-function analyses of either gene do not show any phenotypical change, but the hae hsl2 double mutant shows an abscission-defect phenotype. Examination of the abscission zone by light and scanning electron microscopy showed that the abscission zone in the hae hsl2 appears structurally normal. The force required to remove the petals in wild type and hae hsl2 flowers was measured using a petal breakstrength meter. The force required to remove petals from the hae hsl2flowers at all stages of development was similar to that of wild type flowers that have not yet begun to abscise their petals. Taken together, these data support the role of HAE and HSL2 in the activation of cell separation, rather than differentiation of the abscission zone. Ethylene is also known to promote abscission; therefore we tested the ethylene-induced triple response and the effect of exogenous treatment on floral organ in the hae hsl2, revealing that HAE and HSL2 act independently of ethylene. This implies that the HAE is critical for floral abscission in concert with the action of HSL2.

Recent studies revealed that about 240 species in the tribe Brassiceae are derived through diploidization process from an ancient hexaploid after divergence with Arabidopsis. Most triplicates in Brassica genome show sequence-level co-linearity with a counterpart Arabidopsis sequence. We have obtained 91,511 BAC end sequences (BES) and high-resolution fingerprints (SNapShot) from 99,456 BAC clones originated three BAC libraries (HindIII, BamHI, and Sau3AI). All BESs were used for comparative genome analysis with the Arabidopsis. A total of 47,748 (52%) BESs show significant hit (E-6) with at least one spot of Arabidopsis chromosomes. And a total of 4,647 BAC clones (10%) are mapped on the counterpart Arabidopsis chromosomes by directional matches of both ends (9,294 BES) within 30-500 kb interval on Arabidopsis chromosome. These 4,647 clones span 92 Mb of Arabidopsis genome. We have selected a total of 629 BACs that span 86 Mb Arabidopsis genome with minimally comparative overlap (comparative-tile). Up to now, about 600 BACs are sequenced and most show co-linearity with the counterparts. Sequence-based genetic mapping of each BAC and their FPC information will be used as step-stone for walking and construction physical map of all chromosomes. Up to now, 513 BACs are sequence-based anchored on ten B. rapa genetic linkage groups that provide successful information as seed BACs for further extending to close clone gaps between the adjacent seed BACs and thus to complete sequencing of the individual chromosome. We are sequencing cytological chromosome 1 (R9) and 2 (R3), until now we finished about 50% of each chromosome. We also analyzed 130,000 ESTs from 29 cDNA libraries made with various tissues at various developing stage and treatments. The hybridization results of 24K microarray will be presented. All information will be provided to Multinational Brassica Genome Project (MBGP) members, soon, using web-based tool from our Arabidopsis-Brassica Genome Browser (www.brassica-rapa.org).