Ayan Sadhukhan

Repeated fed-batch process for improving lovastatin production.

Abstract Submerged cultivation of a high yielding strain of Aspergillus terreus DRCC 122 for the production of lovastatin in the batch process had limited success with a maximum titre of 1270 mg l −1 in 288 h and an overall volumetric productivity of 4.41 mg l −1 h −1 in a 1000 l bioreactor. A cost effective repeated fed-batch process with maltodextrin and corn steep liquor feed as carbon and nitrogen sources, respectively, showed a significant increase in lovastatin yield. The final titre was 2200 mg l −1 in 288 h of fermentation, with overall volumetric productivity of 7.64 mg l −1 h −1 , showing an increase of 73% over the batch process. The kinetic parameters were studied; maximum specific oxygen uptake rate ( Q O 2 ) and volumetric mass transfer coefficient ( K L a) were 0.24 m mole O 2 g −1 dry cell wt. h −1 and 280 h −1 , respectively, in fed-batch process.

Molecular mechanistic model of plant heavy metal tolerance

Plants being sessile are susceptible to heavy metals (HMs) toxicity and respond differentially to hostile environments. The toxicity of HM is governed by the type of ion and its concentration, plant physiology and stage of plant growth. Plants counteract the HMs stress by overexpressing numerous stress related proteins, glutathione mediated tolerance pathways and signaling proteins involving networks of various stress regulations. Though the response may vary and be specific in its stress networks regulation for each HM. The intricacy of HM tolerance response involves the set of molecular regulation, which demands to be understood to yield HM tolerant plant. Topical advancements in molecular biology and genomics have facilitated studies in transcriptomics and proteomics to identify regulatory genes implied in HM tolerance in plants. The integration of resources obtained through these studies will be of extreme significance, combining the diverse fields of plant biology to dissect the actual HM stress response network. In this review, we put an endeavor to describe the specific aspects of the molecular mechanisms of a plant response to HMs which may contribute to better understanding of the mode of HMs action and overlaps in metal sensing and signaling/crosstalk to other stresses.

Transcriptional Regulation of Aluminum-Tolerance Genes in Higher Plants: Clarifying the Underlying Molecular Mechanisms

Aluminum (Al) rhizotoxicity is one of the major environmental stresses that decrease global food production. Clarifying the molecular mechanisms underlying Al tolerance may contribute to the breeding of Al-tolerant crops. Recent studies identified various Al-tolerance genes. The expression of these genes is inducible by Al. Studies of the major Arabidopsis thaliana Al-tolerance gene, ARABIDOPSIS THALIANA ALUMINUM-ACTIVATED MALATE TRANSPORTER 1 (AtALMT1), which encodes an Al-activated malate transporter, revealed that the Al-inducible expression is regulated by a SENSITIVE TO PROTON RHIXOTOXICITY 1 (STOP1) zinc-finger transcription factor. This system, which involves STOP1 and organic acid transporters, is conserved in diverse plant species. The expression of AtALMT1 is also upregulated by several phytohormones and hydrogen peroxide, suggesting there is crosstalk among the signals involved in the transcriptional regulation of AtALMT1. Additionally, phytohormones and reactive oxygen species (ROS) activate various transcriptional responses, including the expression of genes related to increased Al tolerance or the suppression of root growth under Al stress conditions. For example, Al suppressed root growth due to abnormal accumulation of auxin and cytokinin. It activates transcription of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 and other phytohormone responsive genes in distal transition zone, which causes suppression of root elongation. On the other hand, overexpression of Al inducible genes for ROS-detoxifying enzymes such as GLUTATHIONE–S-TRANSFERASE, PEROXIDASE, SUPEROXIDE DISMUTASE enhances Al resistance in several plant species. We herein summarize the complex transcriptional regulation of an Al-inducible genes affected by STOP1, phytohormones, and ROS.

Joint genetic and network analyses identify loci associated with root growth under NaCl stress in Arabidopsis thaliana

Plants have evolved a series of tolerance mechanisms to saline stress, which perturbs physiological processes throughout the plant. To identify genetic mechanisms associated with salinity tolerance, we performed linkage analysis and genome-wide association study (GWAS) on maintenance of root growth of Arabidopsis thaliana in hydroponic culture with weak and severe NaCl toxicity. The top 200 single-nucleotide polymorphisms (SNPs) determined by GWAS could cumulatively explain approximately 70% of the variation observed at each stress level. The most significant SNPs were linked to the genes of ATP-binding cassette B10 and vacuolar proton ATPase A2. Several known salinity tolerance genes such as potassium channel KAT1 and calcium sensor SOS3 were also linked to SNPs in the top 200. In parallel, we constructed a gene co-expression network to independently verify that particular groups of genes work together to a common purpose. We identify molecular mechanisms to confer salt tolerance from both predictable and novel physiological sources and validate the utility of combined genetic and network analysis. Additionally, our study indicates that the genetic architecture of salt tolerance is responsive to the severity of stress. These gene datasets are a significant information resource for a following exploration of gene function.

Cowpea [Vigna unguiculata (L.) Walp].

Agrobacterium tumefaciens-mediated transformation is an efficient method for incorporating genes and recovering stable transgenic plants in cowpea because this method offers several advantages such as the defined integration of transgenes, potentially low copy number, and preferential integration into transcriptional active regions of the chromosome. Cotyledonary node explants of cowpea present an attractive target for T-DNA delivery followed by regeneration of shoots via axillary proliferation without involvement of a de novo regeneration pathway. In this chapter, we describe a detailed protocol for Agrobacterium-mediated transformation of the cowpea variety Pusa Komal. The seedling cotyledonary node explants are used for cocultivation with an Agrobacterium strain EHA105 harboring standard binary vector, pCAMBIA2301 or pNOV2819, and putative transformed plants are selected using aminoglycoside antibiotic or mannose as sole carbon source, respectively. The entire process includes explant infection to transgenic seed generation in greenhouse.