文摘
The plastid genome of lettuce (Lactuca sativa L.) cv. Berkeley was site-specifically modified with the addition of three transgenes, which encoded β,β-carotenoid 3,3-hydroxylase (CrtZ) and β,β-carotenoid 4,4-ketolase (4,4-oxygenase; CrtW) from a marine bacterium Brevundimonas sp. strain SD212, and isopentenyl diphosphate isomerase from a marine bacterium Paracoccus sp. strain N81106. Constructed transplastomic lettuce plants were able to grow on soil at a growth rate similar to that of non-transformed lettuce cv. Berkeley and generate flowers and seeds. The germination ratio of the lettuce transformants (T0) (98.8?%) was higher than that of non-transformed lettuce (93.1?%). The transplastomic lettuce (T1) leaves produced the astaxanthin fatty acid (myristate or palmitate) diester (49.2?% of total carotenoids), astaxanthin monoester (18.2?%), and the free forms of astaxanthin (10.0?%) and the other ketocarotenoids (17.5?%), which indicated that artificial ketocarotenoids corresponded to 94.9?% of total carotenoids (230?μg/g fresh weight). Native carotenoids were there lactucaxanthin (3.8?%) and lutein (1.3?%) only. This is the first report to structurally identify the astaxanthin esters biosynthesized in transgenic or transplastomic plants producing astaxanthin. The singlet oxygen-quenching activity of the total carotenoids extracted from the transplastomic leaves was similar to that of astaxanthin (mostly esterified) from the green algae Haematococcus pluvialis.