摘要：
Fumarylacetoacetate hydrolase (FAH) catalyses the final step of the tyrosine degradation pathway, which is essential to animals but was of unknown importance in plants until we found that mutation of Short-day Sensitive Cell Death1 (SSCD1), encoding Arabidopsis FAH, results in cell death under short-day conditions. The sscd1 mutant accumulates succinylacetone (SUAC), an abnormal metabolite caused by loss of FAH. Succinylacetone is an inhibitor of delta-aminolevulinic acid (ALA) dehydratase (ALAD), which is involved in chlorophyll (Chl) biosynthesis. In this study, we investigated whether sscd1 cell death is mediated by Chl biosynthesis and found that ALAD activity is repressed in sscd1 and that protochlorophyllide (Pchlide), an intermediate of Chl biosynthesis, accumulates at lower levels in etiolated sscd1 seedlings. However, it was interesting that Pchlide in sscd1 might increase after transfer from light to dark and that HEMA1 and CHLH are upregulated in the light-dark transition before Pchlide levels increased. Upon re-illumination after Pchlide levels had increased, reactive oxygen species marker genes, including singlet oxygen-induced genes, are upregulated, and the sscd1 cell death phenotype appears. In addition, Arabidopsis WT seedlings treated with SUAC mimic sscd1 in decline of ALAD activity and accumulation of Pchlide as well as cell death. These results demonstrate that increase in Pchlide causes cell death in sscd1 upon re-illumination and suggest that a decline in the Pchlide pool due to inhibition of ALAD activity by SUAC impairs the repression of ALA synthesis from the light-dark transition by feedback control, resulting in activation of the Chl biosynthesis pathway and accumulation of Pchlide in the dark.
摘要：
Fumarylacetoacetate hydrolase participates in positive regulation of salt stress in Arabidopsis. Fumarylacetoacetate hydrolase (FAH) catalyzes the hydrolysis of fumarylacetoacetate into fumarate and acetoacetate, the final step in the Tyr degradation pathway that is essential to animals. However, the Tyr degradation pathway is not well understood in plants. Previously, we found that mutation of the SHORT-DAY SENSITIVE CELL DEATH 1 (SSCD1) gene encoding FAH in Arabidopsis causes spontaneous cell death under short day, which first indicated that the Tyr degradation pathway also plays an important role in plants. In this study, we found that the SSCD1 gene was up-regulated by salt stress, and the sscd1 mutant was hypersensitive to salt stress. However, the double mutant of SSCD1 and HOMOGENTISATE DIOXYGENASE, in which intermediates of the Tyr degradation pathway could not be produced, displayed a normal response to salt stress. Furthermore, the sscd1 mutant showed more accumulation of reactive oxygen species (ROS) and less up-regulation of some ROS-scavenging genes such as ASCORBATE PEROXIDASE 2 and COPPER/ZINC SUPEROXIDE DISMUTASE 1 compared with wild type under salt stress. In addition, SSCD1 expression was also up-regulated by H2O2, and the sscd1 mutant exhibited hypersensitivity to oxidative stress compared with wild type. Taken together, we concluded that loss of FAH in sscd1 leads to the accumulation of Tyr degradation intermediates, which impairs the up-regulation of some ROS-scavenging genes under salt stress, causing more accumulation of ROS, resulting in the hypersensitivity of sscd1 to salt stress.
作者机构：
[Bouphun Tunyaluk; Xu Wei; Jiang Yihe; Zhu Qi] Department of Tea Science, College of Horticulture and Landscape, Hunan Agriculture University, Hu'nan, Changsha, 410128
作者机构：
[朱旗; 吴丹; 姜依何; 赵仁亮; 胥伟] National Research Center of Engineering Technology for Utilization of Botanical Functional Ingredients, Key Lab of Tea Science, Hunan Agricultural University, Changsha, 410128, China;[赵仁亮] College of Horticulture, Henan Agricultural University, Zhengzhou, 450002, China
通讯机构：
Key Lab of Education Ministry for Tea Science, National Research Center of Engineering Technology for Utilization of Botanical Functional Ingredients, Hunan Agricultural University, Changsha, China
作者机构：
[刘泽宇] School of Aeronautics, Northwestern Polytechnical University, Xi'an, China;[朱旗] Horticulture and Landscape College, Hunan Agricultural University, Changsha, China;[刘焱] Hunan Province Key Laboratory of Food Science and Biotechnology, Hunan Agricultural University, Changsha, China;[刘焱; 罗灿] College of Food Science and Technology, Hunan Agricultural University, Changsha, China
通讯机构：
College of Food Science and Technology, Hunan Agricultural University, Changsha, China
