A Novel Cytochrome P450 Is Implicated in Brassinosteroid Biosynthesis via the Characterization of a Rice Dwarf Mutant, dwarf11, with Reduced Seed Length

Abstract

We have characterized a rice (Oryza sativa) dwarf mutant, dwarf11 (d11), that bears seeds of reduced length. To understand the mechanism by which seed length is regulated, the D11 gene was isolated by a map-based cloning method. The gene was found to encode a novel cytochrome P450 (CYP724B1), which showed homology to enzymes involved in brassinosteroid (BR) biosynthesis. The dwarf phenotype of d11 mutants was restored by the application of the brassinolide (BL). Compared with wild-type plants, the aberrant D11 mRNA accumulated at higher levels in d11 mutants and was dramatically reduced by treatment with BL, implying that the gene is feedback-regulated by BL. Precise determination of the defective step(s) in BR synthesis in d11 mutants proved intractable because of tissue specificity and the complex control of BR accumulation in plants. However, 6-deoxotyphasterol (6-DeoxoTY) and typhasterol (TY), but not any upstream intermediates before these compounds, effectively restored BR response in d11 mutants in a lamina joint bending assay. Multiple lines of evidence together suggest that the D11/CYP724B1 gene plays a role in BR synthesis and may be involved in the supply of 6-DeoxoTY and TY in the BR biosynthesis network in rice.

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…Likely due to their low transcript abundance, neither brd1 nor ZmD11 transcripts are detected by in situ hybridization in emerging ligules, although transcripts are observed near the primordial leaf base and in initiating lateral organs, respectively (Figures 5A and 5B). Maize brd1-m1 mutants exhibit enlarged auricles and an indistinct blade-sheath boundary, whereas rice d11 mutants have upright leaves (Tanabe et al, 2005;Makarevitch et al, 2012). Our data reinforce previous findings implicating brassinosteroid biosynthesis during patterning of the blade-sheath boundary in maize.…”

Heterotrimeric G protein α subunit is involved in rice brassinosteroid response

“…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].…”

Isolation and initial characterization of GW5, a major QTL associated with rice grain width and weight

“…The mutant protein encoded by the da1-1 allele has negative activity toward DA1 and a DA1-related protein, and overexpression of da1-1 cDNA dramatically increases the seed and organ size of wildtype plants [15]. In addition, plant hormones and their receptors [16][17][18][19], as well as the nutritional synthesis pathway [20,21], have also been implicated in the development of grain in crops and other plant species. For example, the rice dwarf11 mutant has a defect in a novel cytochrome P450, which shares homology with enzymes involved in brassinosteroid biosynthesis, and bears seeds of reduced length [17].…”

“…In addition, plant hormones and their receptors [16][17][18][19], as well as the nutritional synthesis pathway [20,21], have also been implicated in the development of grain in crops and other plant species. For example, the rice dwarf11 mutant has a defect in a novel cytochrome P450, which shares homology with enzymes involved in brassinosteroid biosynthesis, and bears seeds of reduced length [17]. In maize, the gln1-4 mutant displays reduced kernel size owing to the lossof-function in glutamine synthetase isoenzymes [21].…”