Study On Molecular Mechanism Of SlAQP Mediating Tomato Pedicel Abscission

Abscission is an important biological phenomenon to adapt to the environment and ensure the reproduction.However,abscission often causes serious yield and income reduction in agricultural production.Therefore,it is of great significance to clarify the mechanism of abscission and formulate reasonable agronomic measures to prevent and control abscission.Auxin can delay abscission,while ethylene could depress auxin signal to accelerate abscission.Ethylene action are also know required hydrogen peroxide（H₂O₂）for its role in this procession,but the mechanism is not clear.In this study,"Zhongshu No.6"tomato was used as material,and the mechanism of aquaporins involved in Ethylene Regulation of abscission was clarified through by genetic and biochemical evidence.The main results are as follows:1.Clarification the regulation of osmotic and aquaporins on tomato pedicel abscission.As water potential decrease,depression on abscission was increased.Two different specific aquaporin inhibitors treatment could inhibit abscission significantly.The results indicated aquaporin was involved in abscission of tomato pedicel.2.Identification aquaporins regulated tomato abscission.LC-MS showed that eight AQPs were aboundant in AZ of tomato pedicel.q RT PCR analysis showed that the expression of seven AQPs in AZ was specific significantly up-regulated and inhibited by 1-MCP,which was consistent with the expression pattern of abscission.Seven aquaporins silenced plants were induced by VIGS,and the abscission rate was investigated.The results showed that TRV-slpip1;3,TRV-slpip1;5 and TRV-sltip1;1 lines could inhibit the abscission significantly.It suggested SlPIP1;3,SlPIP1;5 and SlTIP1;1 were the key AQPs involved in the regulation of abscission.3.Analysis the function of SlPIP1;3,SlPIP1;5 and SlTIP1;1.Subcellular localization analysis showed that slpip1;3 and slpip1;5 were located on the plasma membrane,while sltip1;1 was located on the tonoplast membrane.By yeast two hybrid and Bi FC,it was confirmed the interaction between SlPIP1;3 and SlPIP1;5.The results of Xenopus assay showed SlTIP1;1 have the water channel activity and SlPIP1;5 have high efficiently water channel activity.However,SlPIP1;3 lacks the water channel activity in the oocytes.And the interaction between SlPIP1;3 and SlPIP1;5,PIP1;5 and XIP1;2 could enhance the water channel activity.4.Defining mechanism of SlPIP1;3,SlPIP1;5 and SlTIP1;1 regulation of tomato pedicel abscission.SlPIP1;3,SlPIP1;5 and SlTIP1;1 mainly depended on the regulation of cytoplasmic H₂O₂ to affect tomato peticle abscission.There were significant differences betwwen Pf of AZ protoplasts and abscission in Sl AQP knockout plants,indicating that the water transport ability of aquaporins is not the key to the regulation of abscission.The functional analysis of CR-slpip1;3,CR-slpip1;5 and CR-sltip1;1 mutants showed that SlPIP1;1,SlPIP1;5 and SlTIP1;1 mediating abscission by modify H₂O₂ transport into cytoplasm to effect ethylene production and PCD.5.Identification ERF52 regulation of aquaporins expression to involve in abscission.Silencing SlERF52 by VIGS could significantly delay abscission and decrease the expression of SlPIP1;3,SlPIP1;5 and SlTIP1;1.By EMSA and GUS activity analysis,the SlERF52 could directly bind to the AQPs promoter and activate their transcription.6.Stress conditions induced the increase of H₂O₂ in the Thisapoplast,and SlPIP1;3,SlPIP1;5 and SlTIP1;5 mediated H₂O₂ transportation to increase cytoplasmic H₂O₂concentration.High concentration of H₂O₂ in cytoplasm could inhibit auxin signaling and increase ethylene production.Ethylene signal could fine tune regulation of AQPs expression in AZ via SlERF52,indicated ethylene might employ SlPIP1;3,SlPIP1;5 and SlTIP1;1 to transport H₂O₂ in AZs cells depressed auxin signal and enhanced ethylene production to accelerate abscission.This observation significantly advances our knowledge regarding the regulatory aspects of abscission in tomato flower,which are likely relevant to the abscission processes of plants in general.