The Endogenous Synthesis Of Auxin And Cytokinin Controls The Mechanism Of Root De Novo Development

Root is an important organ in plants.It supports the above-group part of plants,and also provides water and nutrition for normal growth and development.Recent years,studies in the model plant Arabidopsis thaliana revealed the cell lineage and molecular mechanism of the primary root and lateral root development based on methods of plant genetics,cell biology,biochemistry and molecular biology,bioinformatics and microscope technologies.However,it is remains unclear about the developmental progresses of adventitious roots.In this study,we used the system of adventitious rooting from Arabidopsis leaf explants to explore the role of auxin and cytokinin biogenesis in adventitious root formation.Auxin(indoleacetic acid,IAA),is produced primarily by two steps of chemical reactions.First,tryptophan is transferred into indole propionic acidis catalyzed by the aminotransferase TAA/SAC family proteins.Next,indole propionic acidis is transferred into IAA catalyzed by flavin monooxygenase which is encoded by YUCCA(YUC).The taa1 mutant showed severely decreased adventitious rooting rate from leaf explants.When we added kyn,the inhibitor of endogenous auxin synthesis,in the medium,we found that adventitious rooting was blocked.In both cases,auxin signaling response was reduced.Therefore,endogenous auxin biogenesis is involved in auxin accumulation during adventitious rooting from leaf explants,and this is a key step for cell fate transition in latter stages.In plants,cytokinin is a kind of derivatives of adenine.It is production by three steps.First,the isopentene group is transferred from the dimethylallyl diphosphate(DMAPP)to Adenosine triphosphate(ATP),Adenosine diphosphate(ADP)or adenosine phosphate(AMP)catalyzed by isopentenyl transferase IPT.Then the isopentene group is hydroxylated by cytochrome mono-oxygenase CYP735 A.Finally,the cytokinin is actives by nucleoside monophosphate phosphoribohydrolase LOG.The cytokinin receptor is located in the membrane of endoplasmic reticulum and actives it downstream signaling pathway by phosphorylation of ARR transcription factors.When we added lovastatin,which is the inhibitor of endogenous cytokinin biosynthesis,the adventitious rooting rate was reduced.Cytokinin pathway mutants also exhibited slower rooting rate.In the mutants background,we found that WUSCHEL RELATED HOMEOBOX 5(WOX5),which is a specific marker for root primordium and the root stem cell niche,had a wider expression pattern than that in the wild type background.The structure of the root apical meristem is also disrupted in these mutants.Therefore,the endogenous cytokinin biosynthesis pathway is involved in the process of adventitious root meristem establishment.This study revealed that biogenesis of auxin and cytokinin is involved in adventitious rooting from Arabidopsis leaf explants.We also discuss about the specific function of plant hormones auxin and cytokinin during adventitious root regeneration.We hope that this study will provide useful information to further study how auxin and cytokinin functions in plant regeneration and adventitious root formation.