Holman Tara J, Jones Peter D, Russell Laurel, Medhurst Anne, Ubeda Tomás Susana, Talloji Prabhavathi, Marquez Julietta, Schmuths Heike, Tung Swee-Ang, Taylor Ian, Footitt Steven, Bachmair Andreas, Theodoulou Frederica L, Holdsworth Michael J
Crop Performance and Improvement Division, Rothamsted Research, Harpenden AL5 2JQ, United Kingdom.
Proc Natl Acad Sci U S A. 2009 Mar 17;106(11):4549-54. doi: 10.1073/pnas.0810280106. Epub 2009 Mar 2.
The N-end rule pathway targets protein degradation through the identity of the amino-terminal residue of specific protein substrates. Two components of this pathway in Arabidopsis thaliana, PROTEOLYSIS6 (PRT6) and arginyl-tRNA:protein arginyltransferase (ATE), were shown to regulate seed after-ripening, seedling sugar sensitivity, seedling lipid breakdown, and abscisic acid (ABA) sensitivity of germination. Sensitivity of prt6 mutant seeds to ABA inhibition of endosperm rupture reduced with after-ripening time, suggesting that seeds display a previously undescribed window of sensitivity to ABA. Reduced root growth of prt6 alleles and the ate1 ate2 double mutant was rescued by exogenous sucrose, and the breakdown of lipid bodies and seed-derived triacylglycerol was impaired in mutant seedlings, implicating the N-end rule pathway in control of seed oil mobilization. Epistasis analysis indicated that PRT6 control of germination and establishment, as exemplified by ABA and sugar sensitivity, as well as storage oil mobilization, occurs at least in part via transcription factors ABI3 and ABI5. The N-end rule pathway of protein turnover is therefore postulated to inactivate as-yet unidentified key component(s) of ABA signaling to influence the seed-to-seedling transition.
N端规则途径通过特定蛋白质底物的氨基末端残基的特性来靶向蛋白质降解。拟南芥中该途径的两个组分，即蛋白酶解6（PRT6）和精氨酰-tRNA：蛋白质精氨酰转移酶（ATE），已被证明可调节种子后熟、幼苗糖敏感性、幼苗脂质分解以及脱落酸（ABA）对种子萌发的敏感性。随着后熟时间的延长，prt6突变体种子对ABA抑制胚乳破裂的敏感性降低，这表明种子对ABA存在一个先前未描述的敏感窗口。外源蔗糖可挽救prt6等位基因和ate1 ate2双突变体根系生长的减少，并且突变体幼苗中脂质体和种子衍生的三酰甘油的分解受到损害，这表明N端规则途径参与了种子油动员的调控。上位性分析表明，PRT6对萌发和植株建立的控制，如以ABA和糖敏感性以及储存油动员为例，至少部分是通过转录因子ABI3和ABI5实现的。因此推测蛋白质周转的N端规则途径会使ABA信号传导中尚未鉴定的关键组分失活，从而影响种子到幼苗的转变。
