The role of Arabidopsis Thaliana ribosomal-protein S6 kinase 1 (AtS6K1) under abiotic stresses

Ribosomal protein S6 kinases (S6K) are a family of highly conserved serine/threonine kinases, encompassing two isoforms in plants known as S6K1 and S6K2. Plant S6Ks maintain a similar structure to mammalian and yeast S6Ks, having a high degree of sequence similarity but varying roles. The primary target of S6Ks is the ribosomal protein S6 that forms part of the 40S ribosomal subunit. As such they function as regulators of cell growth, cell proliferation and stress response by regulating protein synthesis and ribosomal biogenesis. Advances in human S6K research has increased exponentially with little focus on plant protein, leaving a large area of fundamental work to be elucidated. This thesis aims to develop the understanding of plant S6Ks with the structural determination of S6K1. Cloning Arabidopsis plant variant (ATS6k1) constructs in E.coli cells for novel expression. The development of fluorescent tagged AtS6K1 for investigation into AtS6K1 cellular localisation. Analysis of in house generated RNA-Seq data showed S6K1 expression to be significantly down-regulated under Heat stress, clarifying previous studies of temporal differences in S6K1 expression. S6K1 transcription factor targets genes were seen to be differentially expressed, upregulating many RBR1 stress-related genes highly enriched in DNA repair. The weak expression of S6K2 transcription factor ABA target genes helps to confirm S6K2s reduced role under heat stress. However, the limited discovery of ABA stress-regulated genes in the literature restricts the clarification of S6K2s function.