Isolation and Characterization of a Rice (Oryza sativa L.) Mutant Deficient in Seed Phospholipase D, an Enzyme Involved in the Degradation of Oil-Body Membranes
2011
Suzuki, Y. (Yasuhiro)
The use of rice bran for human consumption is severely limited because rice bran oil is rapidly degraded. Triacylglycerols (TAGs) occur in oil bodies, which are bounded by phospholipid membranes. Phospholipase D (PLD) degrades the membranes, releasing TAGs, which are then degraded by lipase to free fatty acids, causing poor bran quality. Since PLD serves as a trigger to initiate lipid degradation and the consequent deterioration of bran quality, I screened mutagenized seed by using anti-PLD polyclonal antibodies and identified a PLD-null rice mutant candidate, ‘03-s108’. PLD enzymatic activity of the 03-s108 bran fraction was less than 1/100 that of ‘Nipponbare’, indicating that 03-s108 is a seed-PLD-null mutant. Genetic analysis of a cross between 03-s108 and a rice cultivar having normal PLD activity revealed that the PLD-null characteristic is controlled by a recessive gene. In addition, I studied the PLD content in maturing and germinating rice seeds of 03-s108 and Nipponbare. In Nipponbare seeds, the PLD protein level detected on western blots increased from 7 to 21 d after flowering then leveled off. In contrast, no PLD was detected throughout the maturation process of 03-s108 seed. During germination, PLD was detected in Nipponbare seedlings but not in those of 03-s108. From these results, I suggest that PLD-null seeds will have improved grain and bran stability. In addition, it appears that PLD may not be necessary for seed maturation or germination.
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