2023-09-29-BIOL254-W11-Notes .docx

LECTURE 4: PRINCIPLES OF PLANT PHYSIOLOGY Lecturer: Dr Claudia Meisrimler Some Receptors Initiate Protein Proteolysis The hormones (red colour) bind to receptors ( green colour), initiating proteolysis of repressors (yellow colour) to activate a transcriptional regulator (blue colour). If the amount...

LECTURE 4: PRINCIPLES OF PLANT PHYSIOLOGY Lecturer: Dr Claudia Meisrimler Some Receptors Initiate Protein Proteolysis The hormones (red colour) bind to receptors ( green colour), initiating proteolysis of repressors (yellow colour) to activate a transcriptional regulator (blue colour). If the amount of hormone is increased, it binds more to the receptor and associate the degradation of the inhibitor domain resulting in the release of the transcription factor. The transcription factor when active bind to the DNA especially at the promoter area. Proteolytic Targets are Covalently Linked to Ubiquitin Ubiquitin is a small protein that targets protein for proteolytic cleavage or degraded. Protein gets degraded when they are linked to 3 ubiquitin. The structure of ubiquitin is simple, the 2 active amino acid that allows the tagging of a protein is Lysin 63 and Lysin 48. Ubiquitin Ligase Complexes – Ubiquitinate Target Protein Ubiquitin function is cleavage or degradation. It has a downstream effect but in the hormone case it is really about degradation. Ubiquitination or Ubiquitin ligase is when ubiquitin is ligated to the target. This type of ligation is different and ligase different things together. Ubiquitin binds to auxin, TIR1, and other molecules. Disrupting hormone synthesis or response interferes with elongation (take note for the exam) Gibberellin increases growth if added to apical meristem of shoots in mutant and in wild type. In the case of auxin, using the Arabidopsis plant. The wild type is usually long, in the mutant, it is not long because the transcription factor for auxin was not expressed. In the case of brassinosteriod, the brassinosteriod biosynthesis mutants produce less of the hormone and it does not grow tall as the wild type. Auxin It is important to growth, phototropism, and gravitropism. It is also important for branching, embryonic patterning , stem cell maintenance and organ initiation that is the formation of new leaves. Auxin was discovered by Charles Darwin. He described the effect of auxin. He studied the ways seedlings bends towards light and this effect is nowadays known to be associated with auxin. Darwin concluded that signal moves through the plant and controls plant in that way. Hormones or signal is associated with plant growth or control of plant growth. Auxin research happened after then a lot. Differential cell growth is because of auxin movement to the shaded side. Auxin accumulation on shaded side stimulates elongation and bending. Auxin does not grow in the direction of light but in the direction of the shaded side. That is why we have curly plants, if we turn it around and around, we get the same thing. Cell length is associated with auxin concentration, longer cell length with higher auxin concentration and lower cell length is associated with lower auxin concentration. Auxin moves in part by a chemiosmotic mechanism. Auxin in the cytoplasm is negatively charged and can get out of the cell being transported out by transporters outside the cell to the roots downwards. This is necessary because auxin is only produced in the shoots. Auxin moves by passive diffusion and movement by transporters as well that is why we say auxin moves by chemiosmotic mechanisms. Polar Auxin Transport Auxin transport out of the cells is controlled by 3 families of transport proteins. These proteins reorganise concentrations. They transport auxin downwards and left to right. Auxin Biosynthesis IAA is the minimalized form of auxin , produced from tryptophan via several semi-independent pathways and one tryptophan independent pathways. Plants have multiple pathways to synthesise auxin, this is because it serves as an insurance, it indicates how important auxin is to the plants. It also indicates that if there is any mutation in any of the pathways the plants can still survive. How do we find out the pathway and synthesis involved in growth of auxin, what type of phenotype do we expect? Mutagenesis is the way to go forward in testing for auxin for areas where genetic engineering and CRISPR is not allowed, following mutagenesis, you then screened for your desired traits. Auxin regulates plant development. Auxin is one of the hormones that suppresses branching that is when you trim a tree the auxiliary shoot meristem is cut off and the tress start to branch out. Auxin is also involved in patterning and vascular development. Auxin promotes branching in the roots. Genes are controlling cell growth, signalling, and coordinating other hormones pathways are caused or regulated by auxins.