Study On The LRR Receptor-like Kinase Family In Arabidopsis And Tobacco And Their Role In Regulating Leaf Senescence

Senescence is a developmentally programmed degeneration process and s a combination of complex physiological,biochemical and molecular events.There exist two types of senescence in plants,mitotic senescence e.g.meristem arrest and post mitotic senescence e.g.leaf senescence.Like other senescence events,leaf senescence is the final phase of development,during which cells undergo distinct metabolic and structural changes leading to cell death.The major sign of leaf senescence is the color change from green to yellow.Leaf senescence is an important trait that allows nutrient recycling in plants,improves crop production,helps in pest,disease and drought control and finally in some economical crops like tobacco,senescent leaves are the harvest for that crop.The definite signal responsible for the activation of senescence is still unknown.However it has been demonstrated that a number of internal and external factors like age of plant,development cues,hormones effect and environmental changes are involved in controlling senescence.This research project is designed to understand the molecular basics of leaf senescence in model plant Arabidopsis.The main objective of the research work is to identify genes of LRR-RLKs gene family involved in the regulation of leaf senescence in Arabidopsis and Genome wide identification of tobacco LRR-RLKs gene family members.To achieve the desire results,two individual experiments were conducted.1)Screening of Arabidopsis TDNA lines(LRR-RLKs)for identification of senescence mutants.How senescence signals are perceived by the cell? This signaling mechanism is of great importance for senescence processes.Cell surface receptor kinases may assist in signaling.Genes encoding protein kinases and phosphatases like receptor like kinases(RLKs)are up regulated during senescence indicating that kinase signaling pathways function in perception and transduction of signals during senescence.Receptor like kinases(RLKs)are transmembrane proteins with an extracellular(variable)and an intracellular kinase domain Leucine rich repeat receptor like kinases(LRR-RLKs)are one of the most important class of plant RLKs and play a vital role in developmental and defense related processes in plants.However a few LRR-RLKs have been found active during senescence.We used reverse genetic approach in current study to investigate the role of LRR-RLKs gene family members in Arabidopsis during leaf senescence.A library of 63 homozygous T-DNA insertion mutants(LRR-RLKs mutants)was screened for leaf senescence phenotypes.Five novel LRR-RLKs genes were identified in which loss of function indicated altered leaf senescence phenotypes.These genes were named Senescence-regulating Receptor like kinases(SRKs).Out of these 05 lines,4 mutants were found with early senescence phenotypes(SRK1,SRK2,SRK3 and SRK4,),while 1 exhibited delay senescence phenotypes(SRK5).2)Genome wide identification of LRR-RLKs gene family from Nicotiana tabacum.Leucine rich repeat receptor like kinases(LRR-RLKs)are one of the most important and largest class of plant RLKs 223 members in Arabidopsis.LRR-RLKs are distinguished by a consensus sequence consisting of 21-24 repeating leucines that helps in protein-protein interaction or binding of the receptor to extracellular small molecules e.g.peptides or hormones.Known functions of most plant LRR-RLKs indicate that this class of plant receptor like kinase plays important roles in different physiological functions of plant development and growth like disease resistance and pathogen recognition in plants and immune response.LRR-RLKs gene family have been identified in the Arabidopsis,rice,poplar and tomato genomes,but the evolutionary history and identification of corresponding LRR RLKs in tobacco genome has not been studied.We performed bioinformatics analysis for the genome wide identification of this gene family from Nicotiana tabacum.We identified in total 413 putative LRR-RLKs members from Nicotiana tabacum.Further their reliability was confirmed through Pfam and SMART analysis.To elucidate phylogenetic relationship of this family in tobacco,An unrooted phylogenetic tree was constructed based on both LRR domain sequences.