Abstract
Plant peroxisomes are highly dynamic organelles that mediate a suite of metabolic processes crucial to development. Peroxisomes in seeds/dark-grown seedlings and in photosynthetic tissues constitute two major subtypes of plant peroxisomes, which had been postulated to contain distinct primary biochemical properties. Multiple in-depth proteomic analyses had been performed on leaf peroxisomes, yet the major makeup of peroxisomes in seeds or dark-grown seedlings remained unclear. To compare the metabolic pathways of the two dominant plant peroxisomal subtypes and discover new peroxisomal proteins that function specifically during seed germination, we performed proteomic analysis of peroxisomes from etiolated Arabidopsis (Arabidopsis thaliana) seedlings. The detection of 77 peroxisomal proteins allowed us to perform comparative analysis with the peroxisomal proteome of green leaves, which revealed a large overlap between these two primary peroxisomal variants. Subcellular targeting analysis by fluorescence microscopy validated around 10 new peroxisomal proteins in Arabidopsis. Mutant analysis suggested the role of the cysteine protease RESPONSE TO DROUGHT21A-LIKE1 in β-oxidation, seed germination, and growth. This work provides a much-needed road map of a major type of plant peroxisome and has established a basis for future investigations of peroxisomal proteolytic processes to understand their roles in development and in plant interaction with the environment.
Highlights
Plant peroxisomes are highly dynamic organelles that mediate a suite of metabolic processes crucial to development
Fatty acids are first activated into fatty acylCoA esters by the acyl-activating enzyme (AAE)/acylCoA synthetase before entering the b-oxidation cycle, during which an acetyl-CoA is cleaved in each cycle by the successive action of acyl-CoA oxidase (ACX), multifunctional protein (MFP), and 3-keto-acyl-CoA thiolase (KAT)
To select a developmental stage that yields an adequate amount of tissue for organelle isolation and coincides with the peak activity of peroxisomes, we monitored the activity of isocitrate lyase (ICL), a marker enzyme for peroxisomes in seeds and early seedlings, in 3- to 6-d-old dark-grown Arabidopsis seedlings
Summary
Plant peroxisomes are highly dynamic organelles that mediate a suite of metabolic processes crucial to development. To compare the metabolic pathways of the two dominant plant peroxisomal subtypes and discover new peroxisomal proteins that function during seed germination, we performed proteomic analysis of peroxisomes from etiolated Arabidopsis (Arabidopsis thaliana) seedlings. Glyoxysomes are located in storage organs such as fatty seedling tissues and play a major role in converting fatty acids to sugar; leaf peroxisomes are involved in photorespiration; and nonspecialized peroxisomes exist in other plant tissues and perform unknown functions. Lipid mobilization through fatty acid b-oxidation and the glyoxylate cycle is the main function for peroxisomes in seeds and germinating seedlings In this process, fatty acids are first activated into fatty acylCoA esters by the acyl-activating enzyme (AAE)/acylCoA synthetase before entering the b-oxidation cycle, during which an acetyl-CoA is cleaved in each cycle by the successive action of acyl-CoA oxidase (ACX), multifunctional protein (MFP), and 3-keto-acyl-CoA thiolase (KAT). Products of the glyoxylate cycle exit the peroxisome, enter gluconeogenesis, and are further converted to hexose and Suc to fuel the postgerminative development of seedlings (Penfield et al, 2006)
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