Chloroplast Transformation with Modified accD Operon Increases Acetyl-CoA Carboxylase and Causes Extension of Leaf Longevity and Increase in Seed Yield in Tobacco

Abstract

Acetyl-CoA carboxylase (ACCase) in plastids is a key enzyme regulating the rate of de novo fatty acid biosynthesis in plants. Plastidic ACCase is composed of three nuclear-encoded subunits and one plastid-encoded accD subunit. To boost ACCase levels, we examined whether overexpression of accD elevates ACCase production. Using homologous recombination, we replaced the promoter of the accD operon in the tobacco plastid genome with a plastid rRNA-operon (rrn) promoter that directs enhanced expression in photosynthetic and non-photosynthetic organs, and successfully raised the total ACCase levels in plastids. This result suggests that the level of the accD subunit is a determinant of ACCase levels, and that enzyme levels are in part controlled post-transcriptionally at the level of subunit assembly. The resultant transformants grew normally and the fatty acid content was significantly increased in leaves, but not significantly in seeds. However, the transformants displayed extended leaf longevity and a twofold increase of seed yield over the control value, which eventually almost doubled the fatty acid production per plant of the transformants relative to control and wild-type plants. These findings offer a potential method for raising plant productivity and oil production.

Transplastomic tobacco plants expressing a fatty acid desaturase gene exhibit altered fatty acid profiles and improved cold tolerance

“…Previous engineering of the lipid pathway through plastid transformation has been attempted at the level of fatty acid biosynthesis by boosting the expression of the accD gene encoding the b subunit of acetylCoA carboxylase (Madoka et al 2002). Compared to control plants, transplastomic plants overexpressing the endogeneous plastidial ACCase gene showed higher fatty acid content (particularly trienoic FAs in MGDG) in leaves, extended leaf longevity, and higher seed yield.…”

“…In both the plastid and the endoplasmic reticulum, various specific desaturase enzymes control the insertion of double bonds at different positions of the fatty acid and lipid molecules (Somerville et al 2000). Except for the b subunit of the prokaryotictype plastidial acetyl-CoA carboxylase, whose gene is present in the plastome of most plants, all genes involved in lipid biosynthesis are located in the nucleus and the encoded enzymes, where necessary, are translocated to the plastid by a transit peptide (Madoka et al 2002;Tetlow et al 2005).…”

Analysis of Acetyl Co-A Carboxylase Activity in Marine Diatoms Isolated from Vellar Estuary, Southest Coast of India

“…At pH 7.0 and pH 9.0 acetyl co-A carboxylase activity slightly decreases, minimum activity observed at pH 6.0, 0.012±0.001 in O. aurita and 0.013±0.002 U/ mg protein in C. muelleri. It is believed that acetyl-CoA carboxylase may be the rate-limiting step in the biosynthesis of fatty acids and any change in the activity of acetyl-CoA carboxylase may affect lipid biosynthesis (Ahmad et al, 2000;Madoka et al, 2002). ACCases from algae and the majority of ACCases from higher plants are similar, responsible for both biotin carboxylation and subsequent carboxyl transfer to acetyl CoA (Roessler, 1990).…”

Transplastomic plants for innovations in agriculture. A review

“…The first work dealing with the engineering of the lipid pathway by plastid transformation aimed at replacing the promoter of the endogenous plastid accD gene encoding the β-carboxyl transferase subunit of the key enzyme in de novo fatty acid biosynthesis, namely acetyl-CoA carboxylase (ACCase), in tobacco (Madoka et al 2002). The leaves of transplastomic plants overexpressing the endogenous plastidial ACCase gene under a strong rRNA promoter had an increased leaf longevity reflected as delayed senescence, lower starch content, but higher fatty acid and lipid (monogalactosyldiacylglycerol) content, and altered fatty acid composition with increased unsaturation levels (Table 4) than non-transformed plants.…”

“…The leaves of transplastomic plants overexpressing the endogenous plastidial ACCase gene under a strong rRNA promoter had an increased leaf longevity reflected as delayed senescence, lower starch content, but higher fatty acid and lipid (monogalactosyldiacylglycerol) content, and altered fatty acid composition with increased unsaturation levels (Table 4) than non-transformed plants. The fatty acid content and composition of the seeds remained unchanged in transplastomic plants; however, they had 2-fold higher seed production, resulting in increased seed oil yield per plant (Madoka et al 2002). Other works later successfully improved seed fatty acid composition of tobacco (Craig et al 2008, see Section 3.3.1).…”