次生代谢
多酚氧化酶
苯丙素
生物化学
酶
新陈代谢
生物
次生代谢物
代谢物
选择性氧化酶
氧化酶试验
程序性细胞死亡
化学
生物合成
过氧化物酶
基因
细胞凋亡
作者
Soha Ahmadzadeh Araji,Theresa A. Grammer,Ross Gertzen,Stephen C. Anderson,Maja Mikulič-Petkovšek,Robert Veberič,My L. Phu,A. Solar,Charles A. Leslie,Abhaya M. Dandekar,Matthew A. Escobar
出处
期刊:Plant Physiology
[Oxford University Press]
日期:2014-01-21
卷期号:164 (3): 1191-1203
被引量:167
标识
DOI:10.1104/pp.113.228593
摘要
Abstract The enzyme polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds into highly reactive quinones. Polymerization of PPO-derived quinones causes the postharvest browning of cut or bruised fruit, but the native physiological functions of PPOs in undamaged, intact plant cells are not well understood. Walnut (Juglans regia) produces a rich array of phenolic compounds and possesses a single PPO enzyme, rendering it an ideal model to study PPO. We generated a series of PPO-silenced transgenic walnut lines that display less than 5% of wild-type PPO activity. Strikingly, the PPO-silenced plants developed spontaneous necrotic lesions on their leaves in the absence of pathogen challenge (i.e. a lesion mimic phenotype). To gain a clearer perspective on the potential functions of PPO and its possible connection to cell death, we compared the leaf transcriptomes and metabolomes of wild-type and PPO-silenced plants. Silencing of PPO caused major alterations in the metabolism of phenolic compounds and their derivatives (e.g. coumaric acid and catechin) and in the expression of phenylpropanoid pathway genes. Several observed metabolic changes point to a direct role for PPO in the metabolism of tyrosine and in the biosynthesis of the hydroxycoumarin esculetin in vivo. In addition, PPO-silenced plants displayed massive (9-fold) increases in the tyrosine-derived metabolite tyramine, whose exogenous application elicits cell death in walnut and several other plant species. Overall, these results suggest that PPO plays a novel and fundamental role in secondary metabolism and acts as an indirect regulator of cell death in walnut.
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