Mycobacterium tuberculosis MtrB Sensor Kinase Interactions with FtsI and Wag31 Proteins Reveal a Role for MtrB Distinct from That Regulating MtrA Activities

The septal association of Mycobacterium tuberculosis MtrB, the kinase partner of the MtrAB two-component signal transduction system, is necessary for the optimal expression of the MtrA regulon targets, including ripA, fbpB, and ftsI, which are involved in cell division and cell wall synthesis. Here, we show that MtrB, irrespective of its phosphorylation status, interacts with Wag31, whereas only phosphorylation-competent MtrB interacts with FtsI. We provide evidence that FtsI depletion compromises the MtrB septal assembly and MtrA regulon expression; likewise, the absence of MtrB compromises FtsI localization and, possibly, FtsI activity. We conclude from these results that FtsI and MtrB are codependent for their activities and that FtsI functions as a positive modulator of MtrB activation and MtrA regulon expression. In contrast to FtsI, Wag31 depletion does not affect MtrB septal assembly and MtrA regulon expression, whereas the loss of MtrB increased Wag31 localization and the levels of PknA/PknB (PknA/B) serine-threonine protein kinase-mediated Wag31 phosphorylation. Interestingly, we found that FtsI decreased levels of phosphorylated Wag31 (Wag31∼P) and that MtrB interacted with PknA/B. Overall, our results indicate that MtrB interactions with FtsI, Wag31, and PknA/B are required for its optimal localization, MtrA regulon expression, and phosphorylation of Wag31. Our results emphasize a new role for MtrB in cell division and cell wall synthesis distinct from that regulating the MtrA phosphorylation activities.     

Lead and cadmium content of Indian flue-cured tobacco

Summary Studies on levels of lead and cadmium of Indian flue-cured tobacco indicated that the leaf contained very low amounts of these heavy metals as compared to tobacco from other countries. Indian tobacco can therefore be adjudged as ‘safe and clean’ and least hazardous to the smoker. Of the two heavy metals, lead content of soils is higher than cadmium. But in the leaf, cadmium content is more than lead indicating that soil cadmium may be more available to tobacco and hence more readily absorbed by the plant than lead.     

Selection intensities and consanguineity in the Yadava and Vadabalija of Visakhapatnam, Andhra Pradesh, India.

The opportunity for intensity of selection is studied in two backward caste groups with different occupations, namely Yadava (pastoral) and Vadabalija (fishing) of Bheemunipatnam Taluk of Visakhapatnam District, Andhra Pradesh. The amount of selection intensity is found to be higher in Vadabalija (0.8583) than Yadava (0.5827). The contribution of mortality to the total index of selection is greater in Vadabalija (0.6095) than in Yadava (0.3326). When consanguineity is considered, the fertility components of selection intensity (0.1885) are lower in the consanguineous group of Yadava than in the nonconsanguineous group (0.2845), whereas in Vadabalija they are higher in the consanguineous group (0.5261) than in the nonconsanguineous group (0.2223).     

A comparative analysis of biparental mating and selfing in pearl millet (Pennisetum typhoïdes) S & H

Summary A study was made of the nature of variation and changes in association for characters related to yield, development and disease resistance in two sets of progenies one set derived through biparental mating (A-series) and the other by traditional inbreeding (selfing) from the F₂ onwards (T-series), in a 22 × 22 diallel of dwarf derivatives of Pennisetum typhoides S & H. Comparison of means and variances within and between the two groups of progenies (A and T-series) and with those of released hybrids (HB-1, HB-2, HB-3, HB-4) for seventeen characters (six related to development, six to productivity, three to vegetative growth and one each to earliness and disease incidence) showed significant variation among the lines of the two series for synchrony of tillering, earliness, disease incidence, chlorophyll depth, grain hairiness, tiller number, plant height, length of earhead, grain yield and grain weight. The A-series selections were significantly superior to the T-series for most of the characters, indicating the effectiveness of selection in biparental matings compared with selection in selfed progenies for these traits. Many of the A-series (220 out of 800) selections were also superior to the existing released hybrids.Changes in the magnitude and nature of association among twelve important characters in the two populations were more favourable in the biparental matings: of 66 possible correlation coefficients examined, 25 cases were found with changes in favour of selections from biparental matings (A-series). These changes were probably due to the breakage of unfavourable linkages and changes in phase of linkage, and indicate the usefulness of biparental matings in the simultaneous improvement of the population for several attributes.     

Mycobacterium tuberculosis cells growing in macrophages are filamentous and deficient in FtsZ rings

FtsZ, a bacterial homolog of tubulin, forms a structural element called the FtsZ ring (Z ring) at the predivisional midcell site and sets up a scaffold for the assembly of other cell division proteins. The genetic aspects of FtsZ-catalyzed cell division and its assembly dynamics in Mycobacterium tuberculosis are unknown. Here, with an M. tuberculosis strain containing FtsZ(TB) tagged with green fluorescent protein as the sole source of FtsZ, we examined FtsZ structures under various growth conditions. We found that midcell Z rings are present in approximately 11% of actively growing cells, suggesting that the low frequency of Z rings is reflective of their slow growth rate. Next, we showed that SRI-3072, a reported FtsZ(TB) inhibitor, disrupted Z-ring assembly and inhibited cell division and growth of M. tuberculosis. We also showed that M. tuberculosis cells grown in macrophages are filamentous and that only a small fraction had midcell Z rings. The majority of filamentous cells contained nonring, spiral-like FtsZ structures along their entire length. The levels of FtsZ in bacteria grown in macrophages or in broth were comparable, suggesting that Z-ring formation at midcell sites was compromised during intracellular growth. Our results suggest that the intraphagosomal milieu alters the expression of M. tuberculosis genes affecting Z-ring formation and thereby cell division.     

Effect of X-radiation on pollen tube growth and seed setting in crosses between Nicotiana tabacum and N. rustica

Summary In vitro andin vivo studies of the effect of irradiating pollen with different doses of X-rays were carried out inNicotiana rustica andN. tabacum. Dosages upto 9600 r were found to enhance the rate of growth of pollen tubers per unit time. Advantage was taken of this observation to overcome the incompatibility normally found in the crossN. tabacum x N. rustica as a result of the inadequate growth ofrustica pollen tubes intabacum style. Thus, whenrustica pollen exposed to 4800 r and 9600 r of X-rays were used to pollinatetabacum, fertilization resulting in the formation of viable hybrid seeds occurred. In the crossN. rustica×N. tabacum there is partial seed failure as a result of the hyperplastic development of the nucellar and endothelial cells. However, when X-rayedtabacum pollen were used in the cross, seed development registered a marked improvement. Since there is now evidence for suggesting that the contents of even those pollen tubes which do not participate in fertilization have some role to play in the development of the seed, it seems likely that radiation-induced biochemical changes in pollen may prove advantageous when conditions for seed development are abnormal as in instances of somatoplastic sterility. Besides such indirect biochemical effects, irradiation of pollen may also lead to genetic changes resulting in the inactivation of zygotic lethals. Thus, there is much scope for investigating the use of radiation to overcome inter-specific and inter-generic cross-incompatibility barriers.With 2 Figures in the Text     

A quantitative evaluation of inter-varietal hybrids of Brassica campestris L.

Summary A quantitative evaluation of yield components was carried out in 150 inter-varietal hybrids of Brassica campestris using five each of the three varieties, brown sarson (BS) , yellow sarson (YS) and toria (TR). The results showed both additive and non-additive gene action for plant height, number of primary and secondary branches and number of siliquae on the main axis in all the six cross combinations BS-YS, YS-BS, BS-TR, TR-BS, YS-TR and TR-YS. The general combining abilities of BS, YS and TR indicated that their nature and magnitude depended largely on the other parents which entered the hybrids. There were differences in combining ability between direct and reciprocal combinations. GBS II, Kanpur Lotni 17, Kanpur Lotni 27 and DS 17D in BS, IB 3, IB 5, IB 6 and BP 12 in YS , and T 165, T 244 and T 1842 in TR were identified as potential parents for inter-varietal hybridisation. Reciprocal effects were found when BS or YS was used as parent and they were least when TR was used as a parent. The amount and degree of heterosis was substantial in inter-varietal crosses. Based on the heterosis-combining ability relationship, the role of inter-varietal hybridisation in population improvement of Brassica campestris is discussed. A number of methods of utilising the inter-varietal hybrids in multiple crosses and synthetic complexes is suggested as potential supplements to population breeding in this crop.Part of a Ph.D. thesis submitted by senior author to P.G. School, Indian Agricultural Research Institute, New Delhi     

RNase HI Is Essential for Survival of Mycobacterium smegmatis

RNases H are involved in the removal of RNA from RNA/DNA hybrids. Type I RNases H are thought to recognize and cleave the RNA/DNA duplex when at least four ribonucleotides are present. Here we investigated the importance of RNase H type I encoding genes for model organism Mycobacterium smegmatis. By performing gene replacement through homologous recombination, we demonstrate that each of the two presumable RNase H type I encoding genes, rnhA and MSMEG4305, can be removed from M. smegmatis genome without affecting the growth rate of the mutant. Further, we demonstrate that deletion of both RNases H type I encoding genes in M. smegmatis leads to synthetic lethality. Finally, we question the possibility of existence of RNase HI related alternative mode of initiation of DNA replication in M. smegmatis, the process initially discovered in Escherichia coli. We suspect that synthetic lethality of double mutant lacking RNases H type I is caused by formation of R-loops leading to collapse of replication forks. We report Mycobacterium smegmatis as the first bacterial species, where function of RNase H type I has been found essential.     

Antimicrobial constituents from the rhizomes of Rheum emodi

The bioassay-guided chemical examination of the rhizomes of R. emodi resulted in the isolation of two new oxanthrone esters, revandchinone-1, revandchinone-2, a new anthraquinone ether revandchinone-3 and a new oxanthrone ether, revandchinone-4. Their structures were established based on spectroscopic and degradative evidence. Occurrence of oxanthrone ether is reported for the first time. The anti bacterial and anti fungal activity of the isolates is studied.