Executive Summary : | Global warming due to climate change is one of the major concerns human civilization facing so far. This resulted increase in average temperature which poses threat to survival and distribution of plants on planet earth. Heat stress occurred when temperature is hot enough for sufficient time of the day causing irreversible damage to plant function/development. Heat stress is one of the most damaging stresses threatening plant productivity and yield from tropics to temperate regions of the globe. Heat stress affects overall cellular metabolism by altering membrane fluidity, protein degradation, enzyme inactivation, and the accumulation of reactive oxygen species (ROS) in plant. It is noteworthy to mention that plants are well equipped with defense strategies to adapt heat stress, however, these measures are insufficient to defend the ever-rising temperatures which ultimately cause substantial yield reduction in crop species. It is well known fact that heat stress disrupts electron transport, enhances ROS production in chloroplast and mitochondria, damages DNA and cell membrane leading to cell death. On the other hand, photosynthesis is very sensitive to high-temperature as it modifies the photochemical reaction in thylakoid lamellae in chloroplasts resulting modification of the electron acceptor site of PSII and a direct effect on photophosphorylation. A moderate rise in temperature (29°C) leads to hypocotyl elongation of seedling (thermomorphogenesis) in model plant Arabidopsis, however, prolonged exposure causes leaf scorching, leaf necrosis, leaf senescence, leaf abscission, reduced root and shoot growth, flower drop and less seed number. Interestingly, some species can distinguish subtle differences of 1°C. However, the mechanisms of temperature perception are largely unknown except the recent characterization of thermosensors such as H2A.Z-containing nucleosomes, phytochrome B and phytochrome interacting factor 4 & 7. In mammals, transient receptor potential channels serves as primary transducers of temperature stimuli or as modulators of signal transduce by other receptors but such channels are missing in Arabidopsis genome. Several reports suggested that photoreceptors act as thermosensors in plant. The Arabidopsis genome contains five loci encoding PhyA, PhyB, PhyC, PhyD and PhyE. Studies have shown that PhyA appears to be the exclusive far red sensor, PhyB is red sensor whereas PhyC, PhyD and PhyE contribute a less prominent role in red light sensing. Few QTL mapping of warm temperature and early flowering also showed PhyC as a potential gene that may contribute to heat stress. However, role of only PhyB is known for ambient temperature sensing in Arabidopsis so far. The present proposal is designed to dissect and investigate the mechanism of thermal signaling by other phytochromes in Arabidopsis. Such knowledge will highly useful in the development of heat tolerant crop varieties in the era of rapid climate change in coming years. |