Untying arsenite tolerance mechanisms in contrasting maize genotypes attributed to NIPs-mediated controlled influx and root-to-shoot translocation, redox homeostasis and phytochelatin-mediated detoxification pathway.

Contamination of ground water and soil with toxic metalloids like arsenic (As) poses a serious hazard to the global agricultural food production. One of the best ways to restrict entry of As into the food chain is selection of germplasms which accrue extremely low level of As in grains. Here, we screened diverse maize genotypes under high arsenite (100 µM AsIII) stress and identified PMI-PV-9 and PMI-PV-3 as AsIII-tolerant and -sensitive maize genotype respectively. Expression of genes associated with As uptake, vacuolar sequestration, biosynthesis of phytochelatins, root-to-shoot translocation, in vivo ROS generation, fine tuning of antioxidant defense system, DNA and membrane damage, H2O2 and superoxide anion (O2•-) levels were compared among the selected genotypes. PMI-PV-9 plants performed much better than PMI-PV-3 in terms of plant growth with no visible symptom of As toxicity. Susceptibility of PMI-PV-3 to AsIII stress may be attributed to comparatively low expression of genes involved in phytochelatins (PCs) biosynthesis. Concomitant decrease in ABCC1 expression might be another key factor for futile sequestration of AsIII into root vacuoles. Moreover, up-regulation of ZmNIP3;1 might contribute in high root-to-leaf As translocation. Substantial spike in H2O2, O2•- and MDA levels indicates that PMI-PV-3 plants have experienced more oxidative stress than PMI-PV-9 plants. Appearance of prominent deep brown and dark blue spots/stripes on leaves as revealed after DAB and NBT staining respectively suggest severe oxidative burst in PMI-PV-3 plants. Marked reduction in DHAR and MDAR activity rendered PMI-PV-3 cells to recycle ascorbate pool ineffectively, which might have exacerbated their susceptibility to AsIII stress. In a nutshell, incompetent PCs mediated detoxification system and disruption of cellular redox homeostasis owing to feeble antioxidant defence system resulting oxidative burst might be the prime reasons behind reduced performance of PMI-PV-3 plants under AsIII stress.

Deciphering ß-tubulin gene of carbendazim resistant Fusarium solani isolate and its comparison with other Fusarium species.

Exploration of molecular structure of ß-tubulin is key to understand mechanism of action of carbendazim since its activity depends on strong binding to ß-tubulin. Resistance against the fungicide is often associated with mutation in ß-tubulin gene. A full-length (1619 bp) ß-tubulin gene has been cloned and sequenced from a carbendazim resistant and a sensitive isolates of F. solani isolated from agricultural fields of Murshidabad (24.23 °N, 88.25 °E), West Bengal, India. Phylogenetic position of the isolates was confirmed using internal transcribed spacer and ß-tubulin gene sequences. In the ß-tubulin based phylogenetic tree, Fusarium species with available data were clustered in nine species complexes and members of both F. solani species complex and F. fujikuroi species complex were distributed into three clades each. The ß-tubulin gene of F. solani was found to be shortest due to least number of non-coding sequences indicating its primitiveness among the Fusarium species. The coding region (G + C 58.54%) was organized into five exons. The protein has 446 amino acid, 49.834 KD molecular weight and 4.64 isoelectric point. Amino acid sequence of the resistant and the sensitive isolates were identical, suggesting that the mechanism of carbendazim resistance in the F. solani isolate was not due to point mutation in ß-tubulin gene. The secondary and tertiary structure of ß-tubulin were similar in all the species except F. oxysporum f.sp. cubense. The identification of binding sites for GDP, carbendazim and α-tubulin would resolve how carbendazim prevents tubulin polymerization. All the data are useful to design tubulin-targeted fungicide with better performance.