Alterations of auxin perception in rolB-transformed tobacco protoplasts. Time course of rolB mRNA expression and increase in auxin sensitivity reveal multiple control by auxin.

Expression and physiological effects of the root-inducing rolB gene of Agrobacterium rhizogenes T-DNA were studied simultaneously in tobacco (Nicotiana tabacum) mesophyll protoplasts. The kinetic study of the expression of rolB mRNA following exogenous auxin application showed that auxin transiently stimulated rolB expression, with mRNA levels starting to accumulate 6 to 9 h after auxin was supplied and increasing 300-fold after 12 to 18 h. The parallel study of the auxin sensitivity of rolB-transformed protoplasts, as assayed by their electrical response to the hormone, showed that the auxin treatment generated an increase in sensitivity by a factor of up to 100,000, whereas in untransformed protoplasts the same auxin treatment induced an increase in auxin sensitivity that never exceeded 30- to 50-fold. This reflects a strong cooperative effect of auxin and rolB in transformed protoplasts. Surprisingly, the maximal increase in sensitivity was observed several hours before the maximal accumulation of rolB mRNA, suggesting that the dramatic control of auxin sensitivity by auxin in rolB-transformed protoplasts requires only low levels of rolB expression. Antibodies directed against ZmER-abp1, the major auxin-binding protein from maize, differentially altered the auxin sensitivity of the electrical response of rolB-transformed and normal protoplasts. This suggests that alterations of the auxin reception-transduction pathway at the plasma membrane of rolB-transformed protoplasts may account for their increased auxin sensitivity.     

Biochemical and genetic analysis of variant C of caprine αs2-casein (Capra hircus)

Two alleles, A and B, were previously described at the goat α_s2-casein locus. Isoelectric focusing allowed us to subdivide the former one in two new alleles, called A and C. Although α_s2-casein C cannot actually be distinguished from its A counterpart by starch or polyacrylamide gel electrophoresis, it differs from the previous allele by a single substitution Lys (A)/Ile (C) at position 167, which was confirmed at the nucleotide level. The frequencies of the three α_s2-casein alleles A, B and C were estimated to be 0.85, 0.04 and 0.11 in the French dairy breeds ‘Alpine’ and ‘Saanen’.     

Transport of zinc and manganese to developing wheat grains

An understanding of the transport pathway used by Zn and Mn to enter developing grains may allow measures to increase the Zn and Mn content of wheat grain grown on Zn/Mn deficient soils. For this reason, transport of Zn and Mn into developing grains of wheat ( Triticum aestivum L. cv. Aroona) was investigated. Detached ears (18–22 days post-anthesis) were cultured for 48 h in a solution containing 185 kBq of ⁶⁵Zn and 185 kBq of ⁵⁴Mn. Transport of ⁶⁵Zn to the grain was unaffected by removal of glumes but was slightly reduced after the lemma was removed. Heat girdling the peduncle slightly reduced the amount of ⁶⁵Zn transported to the grain, whilst heat girdling the rachilla reduced transport of ⁶⁵Zn to the grain to a greater degree, suggesting phloem transport to the rachilla. The transport inhibitor CCCP (carbonyl cyanide m -chlorophenyl hydrazone) blocked ⁶⁵Zn transport to grain but not to lemma and glumes. Removing glumes and lemma and heat girdling the peduncle did not affect transport of ⁵⁴Mn, but transport was slightly affected by heat girdling the rachilla, indicating xylem transport. CCCP blocked transport of ⁵⁴Mn into the grain but not to lemma and glumes. It was concluded that xylem-to-phloem transfer of Zn occurs in the rachis and to a lesser extent in peduncle and lemma. The results suggest that the lemma may be an important site for phloem loading when the concentration of Zn within the xylem is high. The data also suggest that Mn was predominantly translocated to the spikelets in the xylem, but that transport to the grain was dependent upon membrane transport before entering the grain. Phloem loading of Mn into the grain vascular system may have occurred at the site of xylem discontinuity in the floral axis.     

Structural features of the uniporter/symporter/antiporter superfamily.

The uniporter/symporter/antiporter superfamily is an evolutionarily related group of solute transporters. For the entire superfamily, we have used a new predictive program to identify the transmembrane domains. These transmembrane domains were then analyzed with regard to their overall hydrophobicity and amphipathicity. In addition, the lengths of the hydrophilic loops connecting the transmembrane domains were calculated. These data, together with structural information in the literature, were collectively used to produce a general model for the three-dimensional arrangement of the transmembrane domains.     

ComC is required for the processing and translocation of ComGC, a pilin-like competence protein of Bacillus subtilis

ComGC is a cell surface-localized protein required for DNA binding during transformation in Bacillus subtilis. It resembles type IV prepilins in its N-terminal domain, particularly in the amino acid sequence surrounding the processing cleavage sites of these proteins. ComC is another protein required for DNA binding, which resembles the processing proteases that cleave type IV prepilins. We show here that ComGC is processed in competent cells and that this processing requires ComC. We also demonstrate that the PilD protein of Neisseria gonorrhoeae, a ComC homologue, can process ComGC in Escherichia coli, and that the ComC protein itself is the only B. subtilis protein needed to accomplish cleavage of ComGC in the latter organism. Based on NaOH-solubility studies, we have shown that in the absence of ComC, but in the presence of all other competence proteins, B. subtilis is incapable of correctly translocating ComGC to the outer face of the cell membrane. Finally, we show that ComGC can be cross-linked to yield a form with higher molecular mass, possibly a dimer, and present evidence suggesting that formation of the higher mass complex takes place in the membrane, prior to translocation. Formation of this complex does not require ComC or any of the comG products, other than ComGC itself.