An 8.5-kb cosmid containing the KORRIGAN gene complements the cellulose-deficient rsw2-1 mutant of Arabidopsis. Three temperature-sensitive alleles of rsw2 show single amino acid mutations in the putative endo-1,4-␤-glucanase encoded by KOR. The F 1 from crosses between kor-1 and rsw2 alleles shows a weak, temperature-sensitive root phenotype. The shoots of rsw2-1 seedlings produce less cellulose and accumulate a short chain, readily extractable glucan resembling that reported for rsw1 (which is defective in a putative glycosyltransferase required for cellulose synthesis). The double mutant (rsw2-1 rsw1) shows further reductions in cellulose production relative to both single mutants, constitutively slow root growth, and enhanced temperature-sensitive responses that are typically more severe than in either single mutant. Abnormal cytokinesis and severely reduced birefringent retardation in elongating root cell walls of rsw2 link the enzyme to cellulose production for primary cell walls and probably cell plates. The Rsw2 Ϫ phenotype generally resembles the Kor Ϫ and cellulose-deficient Rsw1 Ϫ phenotypes, but anther dehiscence is impaired in Rsw2-1 Ϫ. The findings link a second putative enzyme activity to cellulose synthesis in primary cell walls of Arabidopsis and further increases the parallels to cellulose synthesis in Agrobacterium tumefaciens where the celA and celC genes are required and encode a putative glycosyltransferase and an endo-1,4-␤-glucanase related to RSW1 and KOR, respectively.

Nucleoside modification has been studied in unfractionated tRNA from 11 thermophilic archaea (archaebacteria), including phylogenetically diverse representatives of thermophilic methanogens and sulfur-metabolizing hyperthermophiles which grow optimafly in the temperature range of 56 (Thermoplasma acidophilum) to 105°C (Pyrodictium occultum), and for comparison from the most thermophilic bacterium (eubacterium) known, Thermnotoga narilima (80WC). Nine nucleosides are found to be unique to the archaea, six of which are structurally novel in being modified both in the base and by methylation in ribose and occur primarily in tRNA from the extreme thermophiles in the Crenarchaeota of the archaeal phylogenetic tree. 2-Thiothymine occurs in tRNA from Thermococcus sp., and constitutes the only known occurrence of the thymine moiety in archaeal RNA, in contrast to its near-ubiquitous presence in tRNA from bacteria and eukarya. A total of 33 modified nucleosides are rigorously characterized in archaeal tRNA in the present study, demonstrating that the structural range of posttranscriptional modifications in archaeal tRNA is more extensive than previously known. From a phylogenetic standpoint, certain tRNA modifications occur in the archaea which are otherwise unique to either the bacterial or eukaryal domain, although the overall patterns of modification are more typical of eukaryotes than bacteria.Posttranscriptional processing of tRNA produces a variety of structurally modified nucleosides, some of which have been shown to be associated with a range of biological functions, including maintenance of translational fidelity and efficiency, codon usage, tRNA-protein interactions, and adaptation to cellular stress (9). More than 75 different nucleotides are presently known in tRNA from all sources, with modifications occurring mostly in the base and less commonly by methylation at 0-2' in ribose. Both the chemical nature and sequence locations of individual modifications are highly selective (for reviews, see references 9, 19, and 32), with numerous distinct differences exhibited among the three primary phylogenetic domains, Archaea, Bacteria, and Eucarya (formerly termed archaebacteria, eubacteria, and eukaryotes, respectively [53]). Knowledge of tRNA modification in thermophiles is important as an initial step in understanding structure-stability relationships in the nucleic acids of these remarkable organisms, which grow optimally around the boiling point of water (43), and in identifying domain-or kingdom-specific nucleoside modifications which may serve as phylogenetic markers. Additionally, knowledge of the distributions of modified nucleosides will be useful in later sequencing studies, particularly in avoiding misidentifications when structurally new nucleosides are encountered.Among archaeal microorganisms, tRNA from Halobacterium volcanji has been the most extensively studied (18,20),

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In many biomes, plants are subject to heatwaves, potentially causing irreversible damage to the photosynthetic apparatus. Field surveys have documented global, temperature-dependent patterns in photosynthetic heat tolerance (P ); however, it remains unclear if these patterns reflect acclimation in P or inherent differences among species adapted to contrasting habitats. To address these unknowns, we quantified seasonal variations in T (high temperature where minimal chlorophyll-a fluorescence rises rapidly, reflecting disruption to photosystem II) in 62 species native to 6 sites from 5 thermally contrasting biomes across Australia. T and leaf fatty acid (FA) composition (important for membrane stability) were quantified in three temperature-controlled glasshouses in 20 of those species. T was greatest at hot field sites and acclimated seasonally (summer > winter, increasing on average 0.34 °C per °C increase in growth temperature). The glasshouse study showed that T was inherently higher in species from warmer habitats (increasing 0.16 °C per °C increase in origin annual mean maximum temperature) and acclimated to increasing growth temperature (0.24 °C °C ). Variations in T were positively correlated with the relative abundance of saturated FAs, with FAs accounting for 40% of T variation. These results highlight the importance of both plastic adjustments and inherent differences determining contemporary continent-wide patterns in P .

Initiation of symbiotic nodules in legumes requires cytokinin signaling, but its mechanism of action is largely unknown. Here, we tested whether the failure to initiate nodules in the Medicago truncatula cytokinin perception mutant cre1 (cytokinin response1) is due to its altered ability to regulate auxin transport, auxin accumulation, and induction of flavonoids. We found that in the cre1 mutant, symbiotic rhizobia cannot locally alter acro-and basipetal auxin transport during nodule initiation and that these mutants show reduced auxin (indole-3-acetic acid) accumulation and auxin responses compared with the wild type. Quantification of flavonoids, which can act as endogenous auxin transport inhibitors, showed a deficiency in the induction of free naringenin, isoliquiritigenin, quercetin, and hesperetin in cre1 roots compared with wild-type roots 24 h after inoculation with rhizobia. Coinoculation of roots with rhizobia and the flavonoids naringenin, isoliquiritigenin, and kaempferol, or with the synthetic auxin transport inhibitor 2,3,5,-triiodobenzoic acid, rescued nodulation efficiency in cre1 mutants and allowed auxin transport control in response to rhizobia. Our results suggest that CRE1-dependent cytokinin signaling leads to nodule initiation through the regulation of flavonoid accumulation required for local alteration of polar auxin transport and subsequent auxin accumulation in cortical cells during the early stages of nodulation.