The Effects Of TUB4 On Arabidopsis Growth And Development And The Analysis Of The New Role Of TAO1

In this study,TUB4 and TAO1 were identified as a candidate mutations genes by Map-based cloning,from an EMS-mutagenized Arabidopsis leaf epidermal pavement cells swollen mutant,which was named as ecs1?epidermal cell?.Finally,we confirmed that TUB4 responsible for the abnormal pavement cells shape of ecs1.At the same time,we analysed the novel functions of TAO1 besides disease resistance in Arabidopsis.This study is comprised of two parts.The first part mainly study on the mechanism of the effect TUB4 on epidermal cell morphogenesis in Arabidopsis.Plant cell morphogenesis has a lot of accurate and efficient regulatory mechanisms.Microtubules have long been known to play a key role in plant cell morphogenesis,which are an important signal transduction target to regulate cell expansion and morphogenesis.But how they fulfill this function in cell morphogenesis remains unknown.Many morphological and growth development defects were observed in the ecs1 mutant,including the following as:1.Plant height is decreased,the right-handed helical growth of the stem and root in ecs1.Leaf thickness is increased and leaf color is dark green in rosette leaf of ecs1.Chlorophyll content is also significantly elevated in ecs1.The number of grana lamellae membrane in chloroplast is increased and stroma lamellae distribution is discontinuous in ecs1.2.Average area of pavement cells and mesophyll cells are remarkably enlarged in ecs1.The ploidy levels is elevated and endoreduplication is enhanced in ecs1.The cortical microtubule transversal arrays pattern is altered in hypocotyls epidermal cell of ecs1.Cellulose content is reduced in ecs1,several cellulose synthase,CESA1,CESA4 and CESA5 expression levels is decreased in ecs1.These results indicated that TUB4 mutations might cause aberrant cortical microtubules arrays and cellulose content reduced in ecs1,resulting in cell morphology changed in ecs1.3.The primary root is shorten and thicken in ecs1,and root length is hypersensitive to microtubules interaction drugs,propyzamide and taxol.The root gravitropic is weakened in ecs1.The auxin accumulation is reduced in root tip of ecs1,and auxin accumulation can be restored in root tip with NAA and NPA treatment.PIN1 distribution range is lessened and PIN2 accumulation is increased at root cells membrane in ecs1.Many vesicular trafficking are found in root cells of ecs1,and these vesicular accumulation are insensitivity to BFA treatment in ecs1.Finaly,we confirmed that the cortical microtubules abnormal arrays result in the vesicles trafficking defects in ecs1.To sum up,TUB4 mutation may affect the vesicles transport in the root,lead to the polarity orientation of PIN1 and PIN2 changed at root cells membrane,further resulting in auxin polar distribution altered,finally cause the cortical microtubules arrays alteration in hypocotyls epidermal cell,eventually affect cell morphogenesis and root growth development in ecs1.In the second part,we analysed the novel functions of TAO1 in Arabidopsis.Target of AvrB Operation?TAO1?is a TIR-NB-LRR disease resistance protein that responds to avirulence gene B?avrB?.However,whether TAO1 plays a role in Arabidopsis thaliana development and/or abiotic stress is unknown.Here,we found that TAO1 expression is regulated in a development manner throughout various tissues and organs in Arabidopsis,and that TAO1protein is localized to both the plasma membrane and chloroplasts.Moreover,we showed that three tao1 T-DNA insertion mutants had no significant abnormal phenotype.However,we found that TAO1 expression was up-regulated by ethylene precursor ACC and auxin NAA,but down-regulated by ethylene inhibitor AgNO₃ and auxin inhibitor NPA,suggesting that TAO1 is coordinately regulated by ethylene and auxin.We also found that endogenous ethylene production decreased in TAO1-overexpression lines,but increased in the tao1-10 T-DNA mutant line compared to the wild type,suggesting that TAO1 may be a negative regulator of ethylene signaling.In addition,CHIB,PDF1.2 and ERF1 expression levels are also reduced in TAO1-overexpression lines.These novel characteristics shed new light on the role?s?of TAO1 in Arabidopsis independent of its role in disease resistance.