ABA Regulation Of Autophagy In Arabidopsis

Plants suffer from a variety of biotic and abiotic stresses,during which hormone signaling and autophagic process are activated to enhance the stress tolerance.Autophagy is an important and conversed metabolic process in eucaryon,where cargoes,such as organelles,proteins or even pathogens,are sequestered and delivered to vacuole or lysosome for breaking down.Although the function of autophagy has been widely described in plants,how abiotic stress activate plant autophagy is still largely unknown.ABA,an essential plant hormone,modulates the response to abiotic stress by regulating stomata enclosure and the expression of stress response genes.However,whether ABA signaling regulates other processes to improve stress tolerance is unrevealed.In this study,we explore the ABA regulation of autophagy.The results are as followed:(i)Utilizing con-focal laser scanning microscope,GFP points were observed in GFP-ATG8 a transgenic seedlings after ABA treatment.GFP-ATG8 a transgenic plant was crossed with atg7 or atg10 to generate atg7/GFP-ATG8 a line and atg10/GFP-ATG8 a line.GFP points could not accumulate in atg7/GFP-ATG8 a seedlings and atg10/GFP-ATG8 a seedlings after ABA treatment,indicating that the GFP points observed in GFP-ATG8 a were autophagosomes.Further experiments showed that ABA activates the formation of autophagosomes.(ii)ABA activated the expression of ATG1 a,ATG2,ATG5,ATG7,ATG8 a,ATG10 and ATG13 a.The ABA-activated expression of ATGs was not affected in abi5 but partly inhibited in abi4 while the ABA-activated expression of ATGs was strongly blocked in abi1-1.In addition,the expression of ATG1a、ATG8a and ATG13 a induced by salt stress was partly suppressed in abi1-1.(iii)ABA activated the expression of Sn RK1.1 and Sn RK1.2,which was blocked in abi1-1.To check whether Sn RK1 regulates ABA-induced autophagy,Sn RK1.1 transgenic plant was crossed with GFP-ATG8 a transgenic plant to generate the Sn RK1.1-OE/GFP-ATG8 a line.Root cells of Sn RK1.1-OE/GFP-ATG8 a seedlings accumulated more autophagosomes than GFP-ATG8 a seedlings after ABA treatment,indicating that Sn RK1 is a positively regulator in ABA-induced autophagy.Raptor1,one of the TOR subunits,interacted with Sn RK1.1 and ATG13 a in Yeast Two-Hybrid experiment,implying that Sn RK1.1 may regulate autophagy through suppressing the activity of TORC1.(iv)atg mutants were hypersensitive to ABA during germination and growth.Compared to WT,leaves of atg mutants accumulated more ROS after ABA treatment,indicating that autophagy negatively regulates ROS accumulation generated in ABA signaling pathway.Our results demonstrate that ABA activates Sn RK1 to regulate autophagy in response to abiotic stress.Autophagy negatively regulates ROS accumulation in ABA signaling pathway and the ABA hypersensitivity of atg mutants may result from the massive accumulation of ROS.