Morphological and molecular screening of rice germplasm lines for low soil P tolerance

Phosphorus (P) is an essential macronutrient to all crops including rice and it plays a key role in various plant activities and development. Low availability of P in the soils negatively, influences rice crop growth and causes significant yield loss. In the present study, we characterized a set of 56 germplasm lines for their tolerance to low soil P by screening them at low soil P and optimum soil P levels along with low soil P tolerant and sensitive check varieties. These lines were genotyped for the presence/absence of tolerant allele with respect to the major low soil P tolerance QTL, Pup1, using a set of locus specific PCR-based markers, viz., K46-1, K46-2, K52 and K46CG-1. High genetic variability was observed for various traits associated with low soil P tolerance. The yield parameters from normal and low soil P conditions were used to calculate stress tolerance indices and classify the genotypes according to their tolerance level. Out of the total germplasm lines screened, 15 lines were found to be tolerant to low soil P condition based on the yield reduction in comparison to the tolerant check, but most of them harbored the complete or partial Pup1 locus. Interestingly, two tolerant germplasm lines, IC216831 and IC216903 were observed to be completely devoid of Pup1 and hence they can be explored for new loci underlying low soil P tolerance.

     

N-terminal myristoylation alters the calcium binding pathways in neuronal calcium sensor-1

Neuronal calcium sensor-1 (NCS-1) interacts with many membranes and cytosolic proteins, both in a Ca²⁺-dependent and in a Ca₂₊-independent manner, and its physiological role is governed by its N-terminal myristoylation. To understand the role of myristoylation in altering Ca²⁺ response and other basic biophysical properties, we have characterized the Ca²⁺ filling pathways in both myristoylated (myr) and non-myristoylated (non-myr) forms of NCS-1. We have observed that Ca²⁺ binds simultaneously to all three active EF-hands in non-myr NCS-1, whereas in the case of myr NCS-1, the process is sequential, where the second EF-hand is filled first, followed by the third and fourth EF-hands. In the case of myr NCS-1, the observed sequential Ca²⁺ binding process becomes more prominent in the presence of Mg²⁺. Besides, the analysis of ¹⁵N-relaxation data reveals that non-myr NCS-1 is more dynamic than myr NCS-1. The overall molecular tumbling correlation time increases by approximately 20% upon myristoylation. Comparing the apo forms of non-myr NCS-1 and myr NCS-1, we found the possibility of existence of some substates, which are structurally closer to the holo form of the protein. There are more such substates in the case of non-myr NCS-1 than in the case of the myr NCS-1, suggesting that the former accesses larger volumes of conformational substates compared with the latter. Further, the study reveals that the possibility of Ca²⁺ binding simultaneously to different parts of the protein is more favourable in non-myr NCS-1 than in myr NCS-1.     

Structural characterization of an immunoenhancing cytotoxic heteroglycan isolated from an edible mushroom Calocybe indica var. APK2

A water-soluble polysaccharide of an edible mushroom Calocybe indica var. APK2 showed immunoenhancing (macrophage, splenocyte, thymocyte, and bone marrow activation) and cytotoxic activity toward HeLa cell lines and found to consist of d-glucose, d-galactose, and l-fucose in a molar ratio of nearly 3:1:1. On the basis of acid hydrolysis, methylation analysis, and NMR studies (¹H, ¹³C, DEPT-135, TOCSY, DQF–COSY, NOESY, ROESY, HMQC, and HMBC), the structure of the repeating unit of the fuco-galacto-glucan was established as:     

Structural characterization and study of immunoenhancing and antioxidant property of a novel polysaccharide isolated from the aqueous extract of a somatic hybrid mushroom of Pleurotus florida and Calocybe indica variety APK2

A water-soluble polysaccharide was isolated from the aqueous extract of the fruit bodies of somatic hybrid PCH9FB, obtained through intergeneric protoplast fusion between the strains Pleurotus florida and Calocybe indica var. On the basis of total acid hydrolysis, the polysaccharide was found to contain galactose, fucose, and glucose in a molar ratio of nearly 2:1:2. Methylation analysis and NMR experiments ((1)H, (13)C, DEPT-135, DQF-COSY, TOCSY, NOESY, ROESY, HMQC, and HMBC) showed that the structure of the repeating unit present in the polysaccharide was This molecule showed macrophage, splenocyte, thymocyte activation as well as antioxidant property.     

Breeding lines of the Indian mega-rice variety,MTU 1010, possessing protein kinase <Emphasis Type="Italic">OsPSTOL</Emphasis> (<Emphasis Type="Italic">Pup1</Emphasis>), show better root system architecture and higher yield in soils with low phosphorus

MTU 1010 is a high-yielding mega-variety of rice grown extensively in India. However, it does not perform well in soils with low phosphorus (P) levels. With an objective to improve MTU 1010 for tolerance to low soil P, we have transferred Pup1, a major quantitative trait locus (QTL) associated with tolerance from another mega-variety, Swarna, through marker-assisted backcross breeding (MABB). Foreground selection of the F₁ and backcross plants was performed with the co-dominant, closely linked CAPS marker, K20-2, while two flanking markers RM28011 and RM28157 were utilized for recombinant selection. At each backcross generation, positive plants were also analyzed with a set of 85 parental polymorphic SSR markers to identify the QTL-positive plants possessing maximum introgression of MTU 1010 genome. At BC₂F₁, the best backcross plant was selfed to generate BC₂F₂s. Among them, the plants homozygous for Pup1 (n?=?22) were reconfirmed using the functional marker for Pup1, viz., K46-1, and they were advanced through pedigree method of selection until BC₂F₆ generation. A total of five elite BC₂F₆ lines, possessing Pup1 and phenotypically similar to MTU 1010, were screened in the low soil P plot and normal plot (with optimum soil P levels) during wet season, 2016. All the selected lines showed better performance under low P soil with more number of productive tillers, better root system architecture, and significantly higher yield (>?390%) as compared to MTU 1010. Further, under normal soil, the lines were observed to be similar to or better than MTU 1010 for most of the agro-morphological traits and yield. This study represents the successful application of marker-assisted selection for improvement of tolerance to low soil P in a high-yielding Indian rice variety.     

Improvement of blast resistance of the popular high-yielding,medium slender-grain type,bacterial blight resistant rice variety,Improved Samba Mahsuri by marker-assisted breeding

Improved Samba Mahsuri (ISM) is a popular, high-yielding, bacterial blight resistant rice variety possessing medium-slender grain type. As ISM is highly susceptible to blast disease of rice, through the present study we have transferred two major blast resistance genes, Pi2 and Pi54 into the elite variety by marker-assisted backcross breeding. The two blast resistance genes were transferred to ISM through sets of backcrosses. In every backcross generation, PCR-based markers, specific for the blast resistance genes (Pi2 and Pi54) and bacterial blight resistance genes (Xa21, xa13 and xa5) were utilized for foreground selection, while a set of 144 parental polymorphic SSR markers were used for background selection and backcrossing was carried out until BC₂ generation. A solitary BC₂F₁ plant possessing Pi2 or Pi54 along with Xa21, xa13 and xa5 and >?90% recovery of ISM genome was selected from the two sets of backcrosses were crossed and the intercross F₁s (ICF₁s) thus obtained were selfed to generate ICF₂s. Homozygous ICF₂ plants carrying all the five resistance genes were identified through markers and advanced through selfing till ICF₅ generation by adopting pedigree method of selection. Three best lines at ICF₅, possessing excellent resistance against bacterial blight and blast and closely resembling or superior to ISM in terms of grain quality: yield and agro-morphological traits have been identified and advanced for multi-location trials.     

Agrobacterium tumefaciens divisome proteins regulate the transition from polar growth to cell division

The mechanisms that restrict peptidoglycan biosynthesis to the pole during elongation and re‐direct peptidoglycan biosynthesis to mid‐cell during cell division in polar‐growing Alphaproteobacteria are largely unknown. Here, we explore the role of early division proteins of Agrobacterium tumefaciens including three FtsZ homologs, FtsA and FtsW in the transition from polar growth to mid‐cell growth and ultimately cell division. Although two of the three FtsZ homologs localize to mid‐cell, exhibit GTPase activity and form co‐polymers, only one, FtsZ_AT, is required for cell division. We find that FtsZ_AT is required not only for constriction and cell separation, but also for initiation of peptidoglycan synthesis at mid‐cell and cessation of polar peptidoglycan biosynthesis. Depletion of FtsZ_AT in A. tumefaciens causes a striking phenotype: cells are extensively branched and accumulate growth active poles through tip splitting events. When cell division is blocked at a later stage by depletion of FtsA or FtsW, polar growth is terminated and ectopic growth poles emerge from mid‐cell. Overall, this work suggests that A. tumefaciens FtsZ makes distinct contributions to the regulation of polar growth and cell division.     

Isthmus Dependent Atrial Flutter Cycle Length Correlates with Right Atrial Cross-Sectional Area

Background

Right atrial flutter cycle length can prolong in the presence of antiarrhythmic drug therapy. We hypothesized that the cycle length of right atrial isthmus dependent flutter would correlate with right atrial cross-sectional area measurements.

Methods

60 patients who underwent ablation for electrophysiologically proven isthmus dependent right atrial flutter, who were not on Class I or Class III antiarrhythmic drugs and had recent 2-dimensional echocardiographic data comprised the study group. Right atrial length and width were measured in the apical four chamber view. Cross-sectional area was estimated by multiplying the length and width. 35 patients had an atrial flutter rate ≥ 250 bpm (Normal Flutter Group) and 25 patients had an atrial flutter rate < 250 bpm (Slow Flutter Group).

Results

Mean atrial flutter rate was 283 bpm in the normal flutter group and 227 bpm in the slow flutter group. Mean atrial flutter cycle length was 213 ms in the Normal Flutter Group and 265 ms in the Slow Flutter Group (p< 0.0001). Mean right atrial cross sectional area was 1845 mm² in the Normal Flutter group and 2378 mm² in the Slow Flutter Group, (p< 0.0001). Using linear regression, CSA was a significant predictor of cycle length (β =0.014 p = 0.0045). For every 1 mm² increase in cross-sectional area, cycle length is 0.014 ms longer.

Conclusions

In the absence of antiarrhythmic medications, right atrial cross sectional area enlargement correlates with atrial flutter cycle length. These findings provide further evidence that historical rate-related definitions of typical isthmus dependent right atrial are not mechanistically valid.     

Perspectives and challenges of micro/nanoplastics‐induced toxicity with special reference to phytotoxicity

Plastic pollution has become a global concern for ecosystem health and biodiversity conservation. Concentrations of plastics are manifold higher in the terrestrial system than the aquatic one. Micro/nanoplastics (M/NP) have the ability to alter soil enzymatic system, soil properties and also affect soil borne microorganisms and earthworms. Despite, the knowhow regarding modulatory effects of plastics are acquired from the study on aquatic system and reports on their phytotoxic potentials are limited. The presence of cell wall that could restrict M/NP invasion into plant roots might be the putative cause of this limitation. M/NP inhibit plant growth, seed germination and gene expression; and they also induce cytogenotoxicity by aggravating reactive oxygen species generation. Dynamic behavior of cell wall; the pores formed either by cell wall degrading enzymes or by plant–pathogen interactions or by mechanical injury might facilitate the entry of into roots M/NP. This review also provides a possible mechanism of large sized microplastics‐induced phytotoxicity especially for those that cannot pass through cell wall pores. As M/NP affect soil microbial community and soil parameters, it is hypothesized that they could have the potential to affect N₂ fixation and research should be conducted in this direction. Reports on M/NP‐induced toxicity mainly focused only on one polymer type (polystyrene) in spite of the toxicological relevancies of other polymer types like polyethylene, polypropylene etc. So, the assessment of phytotoxic potential of M/NP should be done using other plastic polymers in real environment as they are known to intract with other environmental stressors as well as can alter the the soil–microbe–plant interaction.