Arabidopsis ABS3 Subfamily Of MATE Transporters Interact With ATG8 To Regulateplant Senescence

Senescence is an important stage of growth and development in plant.It is of great significance to the process of life including reproductive development and seed formation,and is also a key factor affecting crop yield and fruit quality.Plant senescence is intricately regulated by both internal factors and environmental cues.Nutrient deprivations such as the lack of nitrogen and carbon sources induce protein degradation and plant senescence.Autophagy is an evolutionarily conserved cellular degradation pathway in eukaryotes and is closely related to senescence regulation.Autophagy deficiency leads to premature senescence accompanied by accelerated protein degradation through additional catabolic pathways under nutrient deprivation conditions.However,the nature of these pahways remains poorly understood.In this thesis,we show that ABS3(abnormal shoot 3)subfamily MATE(multidrug and toxic compound extrusion)transporters interact with ATG8(autophagy-related protein 8)to promote protein degradation and senescence in Arabidopsis thaliana,uncovering a novel senescence regulation pathway in plants.The major findings are:(1)ABS3 subfamily MATE genes expression promote protein degradation and plant senescence under conditions of natural growth,carbon deprivation and nitrogen starvation..(2)mateq(quadruple loss-of-function mutants of ABS3 subfamily MATE genes)can suppress the accelerated protein degradation and premature senescence phenotypes of autophagy-deficient mutants.This indicates that the ABS3 subfamily MATE proteins initiate and promote carbon deprivation-induced senescence process independent of the autophagy pathway.(3)The ABS3 subfamily MATE proteins localize to late endosomes and interact with the autophagy key protein ATG8 on late endosomes via two conserved ATG8 interacting motifs in ABS3.ATG8-ABS3 interaction is uncoupled from the autophagic function of ATG8 or ABS3 transporter activity.(4)Carbon deprivation induces the trafficking of ABS3 from late endosome to the vacuole for degradation.The function of ABS3 to promote senescence and the vacuolar trafficking of ABS3 depend on ATG8-ABS3 interaction,but this process is independent of autophagy.ATG8-ABS3 interaction promotes senescence which represents the new function of ATG8 besides autophagy.(5)Wheat(Triticum aestivum)TaABS3 is similar to Arabidopsis thaliana ABS3,andinteracts with TaATG8 in late endosomes through two conserved ATG8 interacting motifs to promote protein degradation and plant senescence,indicating that the ATG8-ABS3 interaction paradigm is conserved among dicots and monocots.Based on these findings,a model of ABS3-mediated senescence-promoting pathway and autophagy-mediated senescence-inhibiting pathway sharing ATG8 was established to balance plant senescence regulation.Taken together,our findings uncover a novel conserved senescence regulatory pathway controlled by ATG8-ABS3 interaction,which helps to improve understanding the basic biological process of senescence,and provides a knowledge base for artificially controlling senescence to increase crop yield.