Co-action of ABA, brassinosteriod hormone pathways and differential regulation of different transcript isoforms during cold-and-dark induced senescence in Arabidopsis

Senescence in nature is augmented by multiple abiotic factors such as aging, cold and dark simultaneously. To identify unique components involved in senescence during simultaneous cold and dark conditions (CDC), an experiment was designed in Arabidopsis thaliana (Columbia-0) (At Col-0) to introduce either cold or dark or both CDC simultaneously. Initially, senescence was studied in mutants of light signaling pathway. Further, transcriptome sequencing in At Col-0 leaf samples was done involving transitions in CDC. Leaf senescence under CDC was the balanced action of promotion of senescence due to darkness and retardation of yellowing of leaves including all metabolic activities due to cold. Pathway analysis demonstrated that senescence under CDC was positively regulated by ABA pathway and negatively regulated by brassinosteroid pathway genes. Expression levels of ABA pathway gene Plasma Membrane Associated Ca2+-Binding Protein-2 (AtPCAP2) and brassinosteroid pathway gene Cytochrome P450, Family-708, Subfamily-A, Polypeptide-3 (AtCYP708A3) from NGS and real-time PCR results were associated with progression of senescence under CDC. Specific up-regulation of AtPCAP2 was associated with progress of senescence during CDC probably by destabilizing microtubules. The unique down-regulation of AtCYP708A3 might control the reduced accumulation of non-fluorescent dioxybilin type chlorophyll catabolite (NDCC) leading to retardation of senescence. In this study, differential regulation of different transcript isoforms of the same genes was found. It was suggested that different transcript isoforms due to differential splicing mechanisms and UTR regions of a gene may lead to changes in the interactions with down-stream components resulting in differential response due to a gene during different type of senescence.