A Rice Brassinosteroid-Deficient Mutant, ebisu dwarf (d2), Is Caused by a Loss of Function of a New Member of Cytochrome P450

Abstract

We characterized a rice dwarf mutant, ebisu dwarf ( d2 ). It showed the pleiotropic abnormal phenotype similar to that of the rice brassinosteroid (BR)-insensitive mutant, d61 . The dwarf phenotype of d2 was rescued by exogenous brassinolide treatment. The accumulation profile of BR intermediates in the d2 mutants confirmed that these plants are deficient in late BR biosynthesis. We cloned the D2 gene by map-based cloning. The D2 gene encoded a novel cytochrome P450 classified in CYP90D that is highly similar to the reported BR synthesis enzymes. Introduction of the wild D2 gene into d2-1 rescued the abnormal phenotype of the mutants. In feeding experiments, 3-dehydro-6-deoxoteasterone, 3-dehydroteasterone, and brassinolide effectively caused the lamina joints of the d2 plants to bend, whereas more upstream compounds did not cause bending. Based on these results, we conclude that D2/CYP90D2 catalyzes the steps from 6-deoxoteasterone to 3-dehydro-6-deoxoteasterone and from teasterone to 3-dehydroteasterone in the late BR biosynthesis pathway.

Heterotrimeric G protein α subunit is involved in rice brassinosteroid response

“…The d1 mutant is similar to the wild type in flowering time, whereas d2-1 and d61-1 (BR-deficient and -insensitive mutants, respectively) show delayed flowering time as compared with controls [16,19]. Furthermore, in our studies, the d1 mutant did not display a canonical de-etiolated phenotype, such as unelongated mesocotyls, as did d61-1.…”

“…Both BRinsensitive and -deficient rice mutants display erect leaves [16,19,20]. BR-insensitive mutants d61-1 and d61-2 were found to be less sensitive to BL than the wild type on lamina inclination assay [16].…”

Rice leaf inclination2, a VIN3-like protein, regulates leaf angle through modulating cell division of the collar

“…Rice lamina joint angle increases proportionally to BR levels [11,12], and deficiency of OsDWARF4, a key gene in BR biosynthesis, resulted in increased leaf erectness and enhanced grain yields in dense planting [3]. The erect leaves were also observed in other BR biosynthesis-defective mutants including ebisu dwarf (d2, deficiency of CYD90D2/D2 [10]) and brassinosteroid-deficient dwarf1 (brd1, deficiency of OsDWARF [9]). In addition, the BR signaling-defective mutant d61-7, the weakest mutant of rice BRASSINOSTEROID INSENSITIVE1 (OsBRI1, a protein kinase severing as rice BR receptor), and transgenic rice plants with suppressed expression of OsBZR1 (a transcription factor involved in BR signaling pathway), showed erect leaves [13][14][15].…”

“…To date, several rice mutants with altered leaf inclination or QTLs related to lamina joint angle have been genetically identified [3,[7][8][9][10], and the major detected QTL for leaf angle is tiller angle 1 (ta1) [7,8]. However, the underlying mechanism of the leaf angle alteration has not been clarified.…”

Genetic modification of plant architecture and variety improvement in rice

“…Another classic rice dwarf mutant, d2, was characterized as a BR-deficient mutant (Hong et al, 2003). D2 encodes a new member of the cytochrome P450 family, CYP90D2, which is highly homologous to a BR biosynthetic enzyme that catalyzes the reactions from 6-deoxoteasterone to 3-dehydro-6-deoxoteasterone.…”