Question

plant Physiology

compare and contrast "gain of function" mutations versus " loss of function" for genes invilved in cell signal transcuction

Answer 1

A gain of function mutation is the mutation that confers new or enhanced activity on protein. A gain of mutation in a plant disease resistance gene leads to the constitutive activation of downstream signal transduction pathways in suppresser of npr1-1 constitutive 1. The phytohormone cytokinine is regulator of numerous process in plants. In arabidopsis the cytokinine signal is perceived by three membrane located receptors called Arabidopsis histidine kinase2 (AHK2, AHK3, AHK4 ). Constitutively active gain of function variants of the AHK2, AHK3 genes named repressor of cytokinin deficiency2. It is hypothesised that the structural changes caused by these mutation in the sensory and adjacent transmembrane domain caused by cytokinine binding resulting in propagate the signal across the membrane. Activation of plant immune responses by a gain-of-function mutation in a typical receptors like kinase. A gain of function mutation in Msl10 triggers cell death and wound induced hyperaccumulation of jasmonic acid in Arabidopsis. A dominant gain of function Arabidopsis mutant accelerated cell death (acd6) reveals novel regulation and function of salicylic acid signalling pathway in controlling cell death, defences and cell growth.

Loss of function mutation also called inactivating mutation result in the gene product having less or no function. When the allele has a complete loss of function (null allele), it is often called an amorph or amorphic mutation. Loss of function mutation of single cytokinine receptor gene have no or only weak effect on plant growth indicating strong functional redundancy. Loss of function mutation in negative regulators yield mutants with enhanced pathogens resistance and dwarfism that is usually associated with strong resistance phenotype. Vary rarely, gain of function mutation in positive regulators in the same pathway would yield mutants with similar phenotypes such as snc1. Loss of function mutation in the Ethylene receptor ETR1 cause enhanced sensitivity and exaggerated response to Ethylene in Arabidopsis.