Rubisco without the Calvin cycle improves the carbon efficiency of developing green seeds.
Efficient storage of carbon in seeds is crucial to plant fitness and to agricultural productivity. Oil is a major reserve material in most seeds, and these oils provide the largest source of renewable reduced carbon chains available from nature. However, the conversion of carbohydrate to oil through glycolysis results in the loss of one-third of the carbon as CO2. Here we show that, in developing embryos of Brassica napus L. (oilseed rape), Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase) acts without the Calvin cycle and in a previously undescribed metabolic context to increase the efficiency of carbon use during the formation of oil. In comparison with glycolysis, the metabolic conversion we describe provides 20% more acetyl-CoA for fatty-acid synthesis and results in 40% less loss of carbon as CO2. Our conclusions are based on measurements of mass balance, enzyme activity and stable isotope labelling, as well as an analysis of elementary flux modes.
Schwender
Jörg
J
Plant Biology Department, Michigan State University, East Lansing, Michigan 48824, USA. schwend2@msu.edu
Goffman
Fernando
F
Ohlrogge
John B
JB
Shachar-Hill
Yair
Y
D000105:Acetyl Coenzyme A / Q000378:metabolism; D018533:Biomass; D029688:Brassica napus / Q000196:embryology / Q000201:enzymology / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D003116:Color; D005227:Fatty Acids / Q000096:biosynthesis / Q000378:metabolism; D006019:Glycolysis; D010788:Photosynthesis; D010858:Pigmentation; D010938:Plant Oils / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D012639:Seeds / Q000196:embryology / Q000378:metabolism*
D005227:Fatty Acids; D010938:Plant Oils; D002245:Carbon Dioxide; D000105:Acetyl Coenzyme A; D002244:Carbon; D019289:Pyruvic Acid; D012273:Ribulose-Bisphosphate Carboxylase