The Functional Study Of SMXL4 Involved In Strigolactones Signal Transduction Pathway And Response To Drought In Arabidopsis

Strigolactones(SLs)are a group of recently identified plant hormone that play important roles in seed germination,branching and the ability of tolerance to drought.In Arabidopsis,SMXL6/7/8 are the members of SMXL(SUPPRESSOR OF MORE AXILLARY GROWTH2 LIKE)family and can interact with MAX2(MORE AXILLARY GROWTH2)and D14(DWARF14),and can be ubiquitinated and degradated through the signaling pathway mediated by D14-MAX2.In previous study,we isolated a T-DNA insertion mutant athspr(arabidopsis thaliana heat shock protein related)in C24 ecotype by the promoter trapping technology.At HSPR is involved in stress tolerance by regulating ABA signaling pathway in Arabidopsis,and is the paralog of SMXL4,but the funcion of SMXL4 in strigolactons signaling pathway is unknown.Therefore,the funcion of SMXL4 gene in regulating strigolactons signaling pathway was explored by morphological comparison,physiological and biochemical techniques,observation of scanning electron microscope and laser scanning confocal microscope,genetic hybrids and q RT-PCR,using Col-0,smxl4,max2-1 and smxl4max2-1 as materials.Meanwhile,the role of SMXL4 in drought stress tolerance in Arabidopsis were elucidated,which can provide important information how SMXL4 resist against stress.The main results are as follows:1.smxl4 could partly rescue several max2-1 phenotypes,such as the decrease in the number of banches,hypocotyl length,seed germination rate and cotyledons green rate.Moreover,the expression of strigolactons related gene IAA1(INDOLE-3-ACETIC ACID IN-DUCIBLE1)was down-regulated in smxl4max2-1 double mutant compared to max2-1.Therefore,SMXL4 is a repressor in the strigolactones signal pathway.2.smxl4 mutant showed auxin defective phenotype and was more sensitive to auxin transport inhibitors(NPA and TIBA).The fluorescence intensity of PIN1-GFP and DR5-GFP protein were observably decreased in smxl4 mutant root tips compared to wild type.It is indicated that SMXL4 gene may mediate the growth and development of plants by affecting the auxin polar transport and distribution.3.smxl4 mutant was more sensitive to high concentration of synthetic strigolactones(GR24)than wild type.Compared to wild type,the expressions of DLK2(D14- LIKE2)and KUF1(KAR-UP F-box 1)which were SL-inducible markers were up-regulated after treated with GR24 in smxl4 mutant,suggesting that SMXL4 gene may play a certain role in strigolactones signal.4.smxl3,smxl4 and smxl5 mutants showed the similar sensitivity to high concentration of GR24.Moreover,SMXL3,SMXL4 and SMXL5 genes were down-regulated after treated with GR24 in wild type,which suggested that SMXL3,SMXL4 and SMXL5 genes have functional redundancy.5.Compared with wild type and smxl4 single mutant,smxl4max2-1 double mutant displayed a decrease in drought tolerance due to increasing in the stomatal index and sensitivity of ABA and reducing in expression level of ABA-biosynthesis and stressresponse genes,indicating that SMXL4 and MAX2 can offer plant the ability of tolerance to drought.In summary,SMXL4 has a strong response to strigolactones and plays an important role in the strigolactones signal pathway by controling the function of MAX2.Meanwhile,SMXL4 has functional redundancy with SMXL3 and SMXL5 and also can regulate the growth of plant by affecting the auxin polar transport and distribution.Furthermore,SMXL4 can enhance drought tolerance together with MAX2 by influencing stomatal index,sensitivity of ABA and expressions of drought stress-response genes.