Seed development and hydroxy fatty acid biosynthesis in Physaria lindheimeri

Hydroxy fatty acids (HFAs) are valuable industrial raw materials used in many industries. Physaria lindheimeri accumulates over 80% HFA, in the form of lesquerolic acid (20:1OH), in its seed oil. Understanding the seed development of Physaria lindheimeri is an important step to utilizing this unique wild species as a genetic source of HFAs biosynthesis. The changes of seed growth, lipid accumulation and fatty acid composition during seed development of P. lindheimeri were examined from 14 days after pollination (DAP) to desiccation (56 DAP). The seed development could be divided into three periods. During the early period (14 and 21 DAP), seed rapidly increased in size and fresh weight. In mid-maturation period (28, 35, and 42 DAP), lipids and dry weights accumulated steadily. When seeds developed to late-maturation/desiccation stages (49 and 56 DAP), fresh weight dropped significantly due to water loss, and the dry weight and lipid accumulation reached their maximums. Seed color remained green up to 42 DAP and turned to orange-brown at 49 and 56 DAP. The major fatty acid 20:1OH started accumulation when seeds developed into mid-maturation stage (28 DAP) and the accumulation continued thereafter up to 56 DAP, eventually reaching up to 77% of the total seed oil. The HFA accumulation indicates embryonic storage tissue formation, thus 28 DAP defines a critical time point for seed development entering reserve synthesis and accumulation. The information and knowledge obtained from this study are essential to the success of HFA production using metabolic pathway engineering approaches in commodity oilseed crops.