Evolutionary diversification of satellite DNA sequences from Leymus (Poaceae: Triticeae).

The genus Leymus (lymegrass) comprises about 30 polyploid, perennial, temperate grass species in the tribe Triticeae (family Poaceae). Previous studies indicated a large diversity in the Leymus genome, and therefore, the aim of this study was to isolate new repetitive DNA sequences that can be used for differentiating Leymus species and elucidating their genomic relationships. A C0t-1 DNA plasmid library was generated from genomic DNA of American tetraploid species Leymus triticoides. A family of highly repetitive satellite DNA sequences, designated Lt1, was obtained from this library. The Lt1 family consisted of 380 bp SacI repeating units arranging in tandem arrays. A 120 bp MspI subfamily was discovered within this family, indicating that cytosine methylation may have played an important role in the evolution of satellite sequences. The Lt1 satellite was localized in the subtelomeric heterochromatic blocks of L. triticoides chromosomes, which are present on all chromosomes and often on both arms. The Lt1 sequences are abundant in L. triticoides but absent in its closely related species Leymus racemosus. Significant homology was found between the Lt1 family and numerous repetitive sequences from Poaceae species, indicating that the Lt1 is an ancient family of tandemly repeated sequences in grasses.

The tu8 mutation of Arabidopsis thaliana encoding a heterochromatin protein 1 homolog causes defects in the induction of secondary metabolite biosynthesis.

The tu8 mutant of Arabidopsis thaliana (L.) Heynh. was previously described as deficient in pathogen-induced auxin and glucosinolate (GSL) accumulation, as well as in heat-induced accumulation of cytosolic Hsp90, the latter feature was accom"panied by reduced thermotolerance at higher temperatures. The mutated gene was shown to be a novel allele of TERMINAL FLOWER2, encoding the only Arabidopsis homolog for heterochromatin protein 1 (Kim et al., 2004). In this report, we investigated the influence of heat stress on auxin and GSL content, as well as the accumulation of several secondary metabolites derived from the phenylpropanoid pathway, including anthocyanins and sinapine derivatives, in the mutant tu8. tu8 had less sinapine and sinapoyl esters compared to the wild type. In addition, the induction of sinapine by heat shock in Columbia was not found in tu8. Anthocyanins were also induced by heat stress in wild type plants, whereas tu8 showed only slight induction of these compounds and only at higher temperatures. GSLs were induced at higher temperatures in the wild type, but induction was absent in tu8. Transcript levels known to be involved in IAA/glucosinolate synthesis and metabolism (nitrilase and myrosinase) were examined and both showed developmental regulation, while only nitrilase mRNA levels differed between wild type and mutant seedlings. Treatment of Columbia and tu8 with jasmonic acid (JA), a known inducer of glucosinolates, showed differences between wild type and tu8 with respect to induction of individual GSLs and anthocyanins. However, the transcript level of the TU8/TFL2 gene after heat shock and jasmonate treatment did not change. Loss of function or altered function in the heterochromatin protein most likely lead to the pleiotropic phenotype observed for the tu8 mutant.

Temporal changes in a pink feedlot lagoon.

Temporal changes in a feedlot drainage lagoon with a predominance of the phototrophic purple sulfur bacterium, Thiopedia rosea, were investigated during a 3-year period. The surface protein and bacteriochlorophyll concentrations, which indirectly measure T. rosea abundance, peaked annually during the fall months and coincided with the intensity of pink coloration. Surface bacteriochlorophyll concentration correlated with pH, alkalinity, and protein. The pH range was optimal for the survival of T. rosea. Surface sulfide concentration, which increased over the winter and early spring, reached low levels during the fall months. The most striking pattern to emerge was the marked increase in sulfate concentration that occurred each fall and winter. The protein peaks, which preceded the sulfate peaks, were indicative of the sulfate concentrations that would follow. During 1977 and 1978, the lagoon was essentially anaerobic and provided adequate growth conditions for T. rosea. Above-average precipitation during early 1979 raised the water level and altered the chemistry of the lagoon. Dissolved oxygen was higher during the final year, and, concurrently, concentrations of bacteriochlorophyll declined. Aeration of the lagoon resulted in a decrease in T. rosea.