Characterizing Auxin Biosynthetic Mutants in Arabidopsis thaliana                                     Nicole Colón Carrión...
a bacterium that give rise to hairy                 into IAD in plants since the genes orroot disease in dicot plants, is ...
convertionof IAOX into IAN in           in it synthesis. Analyzing this genes       camalexin biosynthesis (Mano and      ...
V. Discussion                                                              ...
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Literature review - Characterizing auxin biosynthetic mutants in arabidopsis thaliana


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Literature review - Characterizing auxin biosynthetic mutants in arabidopsis thaliana

  1. 1. Characterizing Auxin Biosynthetic Mutants in Arabidopsis thaliana Nicole Colón Carrión University of Puerto Rico, Cayey campus; North Carolina State UniversityIAA, also known as auxin, is a phytohormone that control numerous processes in plant system,such as growth, development and regulation. Several studies has concluded that auxinbiosynthesis is controlled by tryptophan pathway. However its complete pathway and transportis not fully understood. For plants to develop it is needed a fine balance of auxin; too much ourtoo little is bad for the plant development. By understanding how the plant synthesized auxin, wecan get a better understanding of how plants regulate this fine balance. This study aims tounderstand auxin synthesis by identifying the missing genes involved in this pathway usingArabidopsis as plant model.Introduction: Several studies have indicated thatauxinbiosynthesis is controlled by the Arabidopsis thaliana is a small tryptophan independent pathway andflowering plant related to the mustard tryptophan dependent pathway, howeverfamily. This type of family is the most how this pathways work remain poorlywidely distributed; it has approximately 340 understood. Several pathways has beengenera and 3,350 species. Arabidopsisis postulated for Trp-dependent pathway; thehighly distributed around the world, it can indole-3- acetamide, the indole-3-pyruvicbe found in central Asia, Mediterranean acid, the trypthamine, and the indole-3-regions and North and South America. This acetaldoxime pathway. The Trp-plant is highly used as a model organism for independent pathways was postulated inthe study of plant biology, since is the first 1991 but how this pathway designs IAA isplant to have it entire genome sequenced. not well understood. By understanding howStudying Arabidobsis thaliana can help to a plants synthesis this hormone, we couldbetter understanding of plants biological understand better how plants regulate it finesystems. balance. Indole acetic acid, also known asauxin was one of the first hormones to be II. Pathways of auxin biosynthesisdiscovered. It is a phytohormone thatcontrols numerous processes in plantsystems, such as regulation, growth and A) Tryptophan dependent pathwaydevelopment. Indole acetic acid moleculescan inhibit or stimulate the expression of 1. The indole-3-acetamide pathwaycertain genes. Auxin can control plant (IAM)development at all levels; that’s why it isimportant for plants to maintain a balance of The indole-3-acetamineIAA, too much or too little can be fatal for pathway is a bacteria-specificthe plant pathway. Agrobacterium rhizogenes,
  2. 2. a bacterium that give rise to hairy into IAD in plants since the genes orroot disease in dicot plants, is enzymes has not been found. Thethought to induce IAA synthesis. IPA pathway also has it doubts sinceAgrobacterium rhizogenes produce IPA has only been detected inhairy roots were IAA is synthesis Arabidopsis seedlings.from Trp. Tryptophan is convertedinto indole-3-acetamide (IAM) byTrpmonooxygenase enzyme. 3. The tryptamine pathway (TAM)Afterwards, indole-3-acetamidehydrolase encoded by AMl1 gene During the tryptamine pathway,converts IAM into IAA. Indole-3- Trp is converted into TAM byacetamide is found in numerous tryptophan decarboxylase (TDC).plants indicating that IAM- TDC genes also contribute to indoledependent pathway is functional in alkaloid and serotonin biosynthesis.monocots or dicot plants. TAM is oxidated by the amonooxygenase-like enzyme Trp. encoded in the YUCCA gene and • Trp monooxygenase converted into N-hydroxytryptamine. IAM The convertion of TAM into N- • indole-3-acetimide hydrolase - AML1 hydroxytryptamine by the YUCCA IAA gene has been questioned. A study conducted by Trivendale et al. indicated that YUCCA gene does not Figure 1.Shows the tract for play a role in the conversion of TAM auxin biosynthesis in the into N-hydroxytryptamine (Mano indoleindole-3-acetamide and Nemoto, 2011; Trivendale et al., pathway. 2010). This discrepancyletthescientific world doubting thetryptamine pathway as2. The indole-3-pyruvic acid intermediate in IAA biosynthesis. pathway (IPA) 4. The indole 3-aetaldoxime The indole-3-pyruvic acid pathway (IAOX)pathway is important for IAAsynthesis not only in plants but also In the indole-3-aetaldoximefor microorganisms. During the pathway, Trp is oxidized into IAOXindole-3-pyruvic acid pathway, Trp by two P450 monooxygenaseis converted into IPA. Arabidopsis enzymes: CYP79B2 and CYP79B3.seedlings contain the TAA1 gene that IAOX also contributes in theencodes an aminotransferase that is synthesis of indoleglucosinolates andused to converts Trp into IPA. IPA is the alkaloid camalexin. IAOX is thenthen converted into indole-3- converted into IAN by anotheracetaldehyde (IAD). Finally the monooxygenase enzyme:product of IAD oxidation, cause by CYP71A13. According to a studyindole-3-acetaldehyde oxidase, is conducted by Nafisiet. al,IAA. What is still unknown in this CYP71A13 catalyses thepathway is whether IPA is converted
  3. 3. convertionof IAOX into IAN in in it synthesis. Analyzing this genes camalexin biosynthesis (Mano and expression changes in response to this Nemoto, 2011; Nafisiet. al, 2007). environmental signal has been used to Finally IAN is converted into IAA monitor auxin activity in plants. By studying by enzymatic complex NIT1 and NIT2 encoded in Arabidopsis NIT these plant responses, auxin levels and genes. IAOX pathway is not a analyzing the gene expression changes or common in plants since it has only the mutants background, can help to a better been identified in Arabidopsis and understanding of how plants regulates this Brassica, also some genes or fine balance of auxin biosynthesis. enzymes have not been yet identified. IV. Relationship between Ethylene and B) Tryptophan independent pathway Auxin In 1991, another pathway for auxin biosynthesis was postulated. Plant hormones can regulate plant This pathway proposed that indole-3- differentiation, growth and development; glycerol phosphate or indole were they can also affect gene expression. the precursors for this pathway. Ethylene, also known as ACC, is one of the Indole-3- glycerol was converted first five hormones to be discovered and into indole by TSA1 gene and IAA studied; is a gaseous hormone that can was synthesized. However this stimulate plant differentiation, flowering pathway was not really understood since some of its data and gene are opening, fruit ripening, etc. Ethylene is missing. Tryptophan independent synthesized by an amino acid methionine pathway is not one of the most that is later converted into S-adenosyl-L- trusted pathways for auxin methionine, commonly refer as SAM. SAM biosynthesis. is then converted to 1-aminocyclopropane-1- carboxylic-acid by the Aminocyclopropane- 1-carboxylic acid synthase (ACC synthase).III. Regulation of Auxin Biosynthesis Auxin stimulates the production of ethylene by activating this step (Alonso et al., 2007; As time had elapsed, plants had Abel et al. 1995). This state there is andeveloped and evolve new techniques and interaction between this two fine plantsresponses in order to survive. Auxin levels hormone. Preview studies has shown thathave evolved and change in response to the ethylene and auxin can interact with eachchanging environment and conditions. other in order to control hypocotylAuxin biosynthesis is influenced by elongation and root inhibition (Alonso et al.,environmental and developmental signals. 2007;Vandenbussche et al.,2003). It wasAuxin can be monitored by it response to concluded that ethylene and auxin canthis environmental and developmental reciprocally regulate each other biosynthesissignals. They can also be monitored thanks and the identification of some genes involved
  4. 4. V. Discussion x.jsp Auxinbiosynthesis has been studiedfor years; however it is not fully understood.Various experiments hadbeenperformedwithArabidopsis mutant auxin defectivebackgrounds in order to identify genesinvolved in this pathway that will helpunderstandit to a greater extend. By isolatingmutants that can overcome or be moresensitive to auxin deficiency, theidentification of new factors involved in theauxin biosynthetic pathway can bediscovered. Many factors andauxinbiosynthetic genes has been discoveredand their function in plant has been studied;nevertheless there still many informationthat has not been discovered or identified. Itis important to elucidateReferences: Alonso et al. 2007. Multilevel Interaction between Ethylene and Auxin in Arabidopsis Roots. Price, Robert et al., 1994. Arabidopsis. United States of America: Cold Spring Harbor Laboratory Press. Mano, Yoshihiro. Nemoto, Keiichirou. 2012. The pathway of auxin biosynthesis in plants. TAIR. [internet] [2008] USA: Arabidopsis Information Resource (TAIR). Available: