Molecular Stress Response

Categories within Protective and Protected Processes Plant Growth Regulation Environmental Change Gene Expression Signal Transduction Protective Processes Protected Processes ROS and Stress Cell Wall Related Phenylpropanoid Pathway Development Metabolism Chloroplast Associated Carbon Metabolism Respiration and Nucleic Acids Mitochondrion Cells Tissues Cytoskeleton Secretion Trafficking Nucleus Protease-associated

Scenarios for Effect of Abiotic Stress on Plant Gene Expression

Regulatory network of gene expression in response to cold stress and osmotic stress Physiologia Plantarum 126: 62–

A combinatorial network of post-transcriptional and post-translational regulations Plant Science 174 (2008): 420–431

6 Plants respond to stress on a cellular and on the whole plant levels Responses to Biotic and Abiotic stresses are connected genetically: link between biotic and abiotic stress signal transduction and plant development

STIMULUS R R Ca 2+ G-prot Kin Phos TF Plasma membrane Nuclear membrane DNA Signal transduction (Simplified model)

Molecular scheme of abiotic stress signal tansduction pathway in plants CURRENT SCIENCE, VOL. 88, NO. 11, 10 JUNE 2005 Signal Perception Signal Transduction Signal Response

The complexity of the plant responses to different abiotic stresses Wangxia Wang et al., (2003)

General Plant Response Expression of stress inducible gene involved in direct plant protection against stress a. Large number or proteins for enzymatic and structural protein -. Membrane protein -. Enzyme for osmolite biosynthesis and detoxification enzyme b. Other protein for macromolecules protection -. LEA protein -. Chaperone -. m-RNA binding protein A variety of regulatory protein a. transcription factors b. protein kinase c. receptor protein kinase d. ribosomal protein kinase e. Signal transduction kinase

Unique Response 1.Heat schock proteins 2.Osmoprotectant 3.Proline 4.Glycine betaine 5.Trehalose 6.Manitol

Heat shock proteins 1.The synthesis and accumulation of HSP are assumed to play a central role in the heat stress response and in tolerance to high temperature 2.The heat stress response is a highly conserved reaction caused by exposure of an organism tissue or cells to sudden high temperature stress 3.HSPs are located in both cytoplasm and organelles such as nucleus, mitochondria, chloroplast, and endoplasmic reticulum 4.The transcription of HSP genes is controlled by regulatory protein called heat stress transcription factors (HSF) which exist as inactive proteins mostly found in the cytoplasm

Osmoprotectant 1.High soil salinity is one of the important factors that limits distribution and productivity of major crops causing yield losses 2.It reduces the ability to take up water leading to reduction in growth rate 3.Salt stress result in a wide variety of physiological and biochemical change in plants, such as the activation of salt inducing genes such as transcription factors, BZIP, LEA, RING Zinc-finger and large scale production and accumulation of osmolytes 4.Plant accumulates the derivation of those molecular weight solutes to mitigate the detrimental effect of salt stress by lowering the water potential of cell or by protecting various cellular structure and protein during stress

Proline 1.Proline as an amino acid known to occur widely in higher plant in response to abiotic stress (salt/osmolite stress) and normally accumulated in large quantities 2.It contribute to the stabilization of protein, membrane, and sub-cellular structure in cytosol and protecting cellular function

Glycine Betaine 1.Glycine betaine is a fully N-methyl-substituted quaternary ammonium derivative of glycine 2.Glycine betaine is accumulated at high level in response to abiotic stress mainly to osmotic stress 3.Glycine betaine is abundant mainly in chloroplast where it plays a vital in the adjusment and protection of thylakoid membrane to maintain photosynthesis efficiency

Trehalose 1.It is non reducing disaccharide sugar and a compatible solute composed of two molecules of glucose 2.It is well-known as an abiotic stress protectant

Manitol 1.It is widely distributed sugar alcohol 2.It is synthesized in mature leaves 3.It is transported to sink tissue where it can be either stored or oxidized to mannose

Physiological Stress Responses Stress resistance: The ability of the organism to survive at the unfavourable factor

Types of Resistance Stress avoidance Plant reduce the metabolic activity resulting in dormant state upon exposure to extreme stress In the whole growth process does not meet with the face of adversity Stress tolerance Plants have mechanism that maintain high metabolic activity similar to the absence of stress under mild stress and reduced activity under severe stress Plant has a capacity of environmental stress defense, and a variety of physiological processes remain normal ❤❤❤❤

20 Acclimation (Hardening off) Cross Resistance Adaptation Important concepts of stress physiology

Acclimation Inducible responses that enable an organism to tolerate an unfavorable or lethal change in their environment Increased stress tolerance as a result of prior exposure to a stress condition Plant have an incredible ability to adjust physiological and structural attributed on the scale of seconds or seasons within a single genotypes Example: heat shock response

Cross Resistance Tolerance to a usually toxic substance as a result of exposure to a similarly acting substance Tolerance to a stress based on exposure to a previous stress event of a different nature Example: 1.Pesticide 2.Antibiotics

Adaptation Genetically determined level of resistance acquired by a process of selection over many generations Favorable gene combination in plant that inhabit stress full environment Evolutionary changes that enable an organism to exploit a certain niche. These include modification of existing genes, as well as gain/loss of genes. For example: thermo-stable enzymes in organisms that tolerate high temperature

Physiological approach to breeding It has an advantage over empirical for yield per se because it increases the probability of crosses resulting in additive gene action for stress adaptation Individual traits must be conceptualized and defined in term of: a. the stage of development b. specific attribute to the target environment a. Their potential contribution to yield Physiological approach has merit over genetic approach for the very simple reason that there is a lack of in-depth understanding of the genetic basis stress adaptation

Physiological traits associated with grain yield under stress Remobilization of carbohydrates Canopy temperature Ground cover Chlorophyll protection or stay green The relative yield performance of the genotype in stress and favorable conditions seems to be a common starting point in identifying desirable genotypes

Two general approaches to determine physiological traits associated with crop performance under stress conditions 1.Proceed from observed yield different to investigate of possible physiological cause 2.Define an ideotype for a particular stress environment based on understanding of physiological process

Limited success of tranditional breeding approaches for stress tolerance 1.The focus has been on yield rather than on specific traits 2.Difficulties in breeding for tolerance traits, which is included complexities introduced by GEI and the relatively infrequent use of simple physiological traits as measure of tolerance 3.Desired traits can only be introduced from closely related species 4.Physiological traits have been seldom used as true criteria selection, due to the difficulty of their measure on practical breeding programs

Physiological approach of Plant Breeding Ideotype Breeding: Plan of the phenotype of the cultivars that will perform optimally in a specific set of climate, soil, biotic and socio cultural condition

Integrated Stress Breeding Approaches 1.Indentifying stress problem 2.Developing screening technology 3.Indentifying stress tolerance traits and their association yield 4.Screening germplasm for suitable sources of variability of traits 5.Utilization of associated traits in the breeding program

Ideotype breeding aimed at modifying the plant architecture is a time- tested strategy to achieve increases in yield potential. Thus, selection for short statured cereals such as wheat, rice, and sorghum resulted in doubling of yield potential. Yield potential is determined by the total dry matter or biomass and the harvest index (HI). Tall and traditional rices had HI of around 0.3 and total biomass of about 12 tons per hectare. Thus, their maximum yield was 4 tons per hectare. Their biomass could not be increased by application of nitrogenous fertilizers as the plants grew excessively tall, lodged badly and the yield decreased instead of increasing. To increase the yield potential of topical rice it was necessary to improve the harvest index and nitrogen responsiveness by increasing the lodging resistance. This was accomplished by reducing the plant height through incorporation of a recessive gene sd1 for short stature Ideotype Breeding

To increase the yield potential of rice further, a new plant type was conceptualized in 1988 at IRRI. Modern semi-dwarf rices produce a large number of unproductive tillers and excessive leaf area that cause mutual shading, and reduce canopy photosynthesis and sink size, especially when they are grown under direct sowing conditions. To increase the yield potential of these semi-dwarf rices, IRRI scientists proposed further modifications of plant architecture with following characteristics: 1. Low tillering,( 9-10 tillers for transplanted conditions) 2. No unproductive tillers grains per panicle 4. Dark green, thick and erect leaves 5. Vigorous and deep root system Ideotype Breeding

Response 1.Species 2.Genotype 3.Developmental stage