Browsing by Author "Singh, Daljit"

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The role of lectins and HD-ZIP transcription factors in isoprenoid based plant stress responses
(INSA, 2012) Kumari, Sangita; Shridhar, Smriti; Singh, Daljit; Priya, Piyush; Farmer, Rohit; Hundal, Jasreet; Sharma, Priyanka; Bavishi, Krutika; Schrick, Kathrin; Yadav, Gitanjali
It was over half a century ago when the overwhelming array of chemicals found in plants was postulated to be more than just by-products of primary metabolism. Ever since, extensive research has been conducted on plant secondary metabolites which are now known to be the end points of sophisticated survival mechanisms that plants have developed as a response to various kinds of stresses. Stress, defined by its negative effect on the growth and development of an individual, can be internal (metabolic or genetic), external (biotic or abiotic), permanent or acute. To cope, organisms must develop tolerance, resistance or avoidance mechanisms. Isoprenoids, often released as volatiles from plants, constitute the most diverse groups of natural products and play an essential part in plant defense systems, both directly (as emitted volatiles) and indirectly (the principle of inviting friends to feast on foes). Research over the last decade has resulted in a significant improvement in our understanding of the isoprenoid biosynthesis but there remains much to learn about the complex regulatory network controlling the various steps of these pathways and their dynamic co-ordination. Here we identify novel plant proteins and provide a putative role for them in isoprenoid based stress responses, along with insights into future perspectives for research.
Shared functions of plant and mammalian StAR-related lipid transfer (START) domains in modulating transcription factor activity
(BioMed Central Ltd, 2014) Schrick, Kathrin; Bruno, Michael; Khosla, Aashima; Cox, Paige N.; Marlatt, Sara A.; Roque, Remigio A.; Nguyen, Henry C.; He, Cuiwen; Snyder, Michael P.; Singh, Daljit; Yadav, Gitanjali
Background Steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domains were first identified from mammalian proteins that bind lipid/sterol ligands via a hydrophobic pocket. In plants, predicted START domains are predominantly found in homeodomain leucine zipper (HD-Zip) transcription factors that are master regulators of cell-type differentiation in development. Here we utilized studies of Arabidopsis in parallel with heterologous expression of START domains in yeast to investigate the hypothesis that START domains are versatile ligand-binding motifs that can modulate transcription factor activity. Results Our results show that deletion of the START domain from Arabidopsis Glabra2 (GL2), a representative HD-Zip transcription factor involved in differentiation of the epidermis, results in a complete loss-of-function phenotype, although the protein is correctly localized to the nucleus. Despite low sequence similarly, the mammalian START domain from StAR can functionally replace the HD-Zip-derived START domain. Embedding the START domain within a synthetic transcription factor in yeast, we found that several mammalian START domains from StAR, MLN64 and PCTP stimulated transcription factor activity, as did START domains from two Arabidopsis HD-Zip transcription factors. Mutation of ligand-binding residues within StAR START reduced this activity, consistent with the yeast assay monitoring ligand-binding. The D182L missense mutation in StAR START was shown to affect GL2 transcription factor activity in maintenance of the leaf trichome cell fate. Analysis of in vivo protein–metabolite interactions by mass spectrometry provided direct evidence for analogous lipid-binding activity in mammalian and plant START domains in the yeast system. Structural modeling predicted similar sized ligand-binding cavities of a subset of plant START domains in comparison to mammalian counterparts. Conclusions The START domain is required for transcription factor activity in HD-Zip proteins from plants, although it is not strictly necessary for the protein’s nuclear localization. START domains from both mammals and plants are modular in that they can bind lipid ligands to regulate transcription factor function in a yeast system. The data provide evidence for an evolutionarily conserved mechanism by which lipid metabolites can orchestrate transcription. We propose a model in which the START domain is used by both plants and mammals to regulate transcription factor activity.