The apple gene responsible for columnar tree shape reduces the abundance of biologically active gibberellin
Daichi Watanabe, Ikuo Takahashi, Naiyanate Jaroensanti‐Tanaka, Sho Miyazaki, Kai Jiang, Masaru Nakayasu, Masato Wada, Tadao Asami, Masaharu Mizutani, Kazuma Okada, Masatoshi Nakajima
Abstract
SUMMARY Ectopic expression of the apple 2‐oxoglutarate‐dependent dioxygenase (DOX, 2ODD) gene, designated MdDOX‐Co , is thought to cause the columnar shape of apple trees. However, the mechanism underlying the formation of such a unique tree shape remains unclear. To solve this problem, we demonstrated that Arabidopsis thaliana overexpressing MdDOX‐Co contained reduced levels of biologically active gibberellin (GA) compared with wild type. In summary: (i) with biochemical approaches, the gene product MdDOX‐Co was shown to metabolize active GA A 4 (GA 4 ) to GA 58 (12‐OH‐GA 4 ) in vitro . MdDOX‐Co also metabolized its precursors GA 12 and GA 9 to GA 111 (12‐OH‐GA 12 ) and GA 70 (12‐OH‐GA 9 ), respectively; (ii) Of the three 12‐OH‐GAs, GA 58 was still active physiologically, but not GA 70 or GA 111 ; (iii) Arabidopsis MdDOX‐Co OE transformants converted exogenously applied deuterium‐labeled (d 2 )‐GA 12 to d 2 ‐GA 111 but not to d 2 ‐GA 58 , whereas transformants converted applied d 2 ‐GA 9 to d 2 ‐GA 58 ; (iv) GA 111 is converted poorly to GA 70 by GA 20‐oxidases in vitro when GA 12 is efficiently metabolized to GA 9 ; (v) no GA 58 was detected endogenously in MdDOX‐Co OE transformants. Overall, we conclude that 12‐hydroxylation of GA 12 by MdDOX‐Co prevents the biosynthesis of biologically active GAs in planta , resulting in columnar phenotypes.