Effects Of Auxin And Ethylene On Root Growth Adaptation To Different Ambient Temperatures In Arabidopsis Thaliana

Plants are sessile organisms,and temperature is a key environmental factor affecting plant distribution,growth and development.However little is known about the molecular mechanisms underlying such developmental plasticity modulated by temperature.We results show that the Arabidopsis ckrc1-1 mutant is more sensitive to higher temperature and less sensitive to lower temperature than Col-0.At 22 oC and 27 oC,the ckrc1-1 root length is significantly shortened and the root gravity defect is enhanced with improved temperature in comparison to Col-0,changes that can be restored with addition of 1-Naphthaleneacetic Acid(NAA),but not Indole-3-Acetic Acid(IAA)at elevated temperature.Addition of 1-Aminocyclopropane-1-carboxylic acid(ACC)can restored ckrc1-1 root length and root curling at 22 oC and 27 oC,while Aminoethoxyvinylglycine(AVG)can enhance ckrc1-1 root curling and inhibit root length.At 17oC,ckrc1-1 root length is more longer than Col-0,related experiments indicate that auxin,ethylene and polar auxin transport regulate ckrc1-1 response to lower temperature.Comparison of the regulatory mechanisms of ckrc1-1 root growth at different temperatures(17 oC,22 oC,27 oC),show that the interaction between signals(auxin and ethylene)and the effects of downstream genes differ at different temperatures.It appears that in the root,auxin signal increases with increasing temperature from lower to higher temperature,and ethylene signal varies from 17 °C to 22 °C and 22 °C to 27 °C in a "V" trend.Analyzing the length of the meristem zone(MZ)and the cell length of the differentiation zone(DZ)appears that CKRC1 doesn,t play an important role in inhibiting root cell elongation by ethylene at 17 °C,but play an important role at 22 °C and 27 °C.Higher temperature can promote CKRC1-dependent auxin biosynthesis by enhancing ETR1-mediated ethylene signaling.Low temperature-enhanced,ETR1-mediated ethylene signaling could not promote the expression of CKRC1.Though analyzing the phenotype of overexpression lines and mutants,we find that the root growth in aux1 and pin2 is similar to the phenotype of ckrc1-1 which is more sensitive to higher temperature and less sensitive to lower temperature than Col-0.CKRC1,AUX1,and PIN2 regulate root elongation by affecting different regions of the root at different temperatures.AUX1,PIN1 and PIN2 are involved in the ckrc1-1 root gravity response under different temperatures.Further,CKRC1-dependent auxin biosynthesis is critical for maintaining AUX1,PIN1 and PIN2 expression.Our research suggest that the interaction between auxin and ethylene and that the interactionmediated polar auxin transport play important roles during the plant root growth response to different temperatures.