Isolation and Characterization of a Rice Dwarf Mutant with a Defect in Brassinosteroid Biosynthesis

Abstract

We have isolated a new recessive dwarf mutant of rice (Oryza sativa L. cv Nipponbare). Under normal growth conditions, the mutant has very short leaf sheaths; has short, curled, and frizzled leaf blades; has few tillers; and is sterile. Longitudinal sections of the leaf sheaths revealed that the cell length along the longitudinal axis is reduced, which explains the short leaf sheaths. Transverse sections of the leaf blades revealed enlargement of the motor cells along the dorsal-ventral axis, which explains the curled and frizzled leaf blades. In addition, the number of crown roots was smaller and the growth of branch roots was weaker than those in the wild-type plant. Because exogenously supplied brassinolide considerably restored the normal phenotypes, we designated the mutant brassinosteroid-dependent 1 (brd1). Further, under darkness, brd1 showed constitutive photomorphogenesis. Quantitative analyses of endogenous sterols and brassinosteroids (BRs) indicated that BR-6-oxidase, a BR biosynthesis enzyme, would be defective. In fact, a 0.2-kb deletion was detected in the genomic region of OsBR6ox (a rice BR-6-oxidase gene) in the brd1 mutant. These results indicate that BRs are involved in many morphological and physiological processes in rice, including the elongation and unrolling of leaves, development of tillers, skotomorphogenesis, root differentiation, and reproductive growth, and that the defect of BR-6-oxidase caused the brd1 phenotype.

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

“…In addition, increased adaxial cell division, but not cell elongation, in the collar of lc2 further showed that LC2 serves as a negative regulator of cell division at the lamina joint to regulate leaf inclination. Although the numbers of leaf bulliform cells were increased under LC2 deficiency, we propose that this mainly contributes to the leaf rolling phenotype (motor cells have an important role in leaf rolling [1,44]), and the resultant changed physical shape and altered tissue flexibility might not lead to the bending of leaves.…”

“…Quantitative analyses were carried out on the Rotor-Gene real-time thermocycler R3000 (Corbett Research) with Real-Time PCR Master Mix (Toyobo). The primers used were as follows: LC2 (5′-AGC ATC AGC TTT GGA CGA GGA-3′ and 5′-CAG TTG GTG GAA TAG AGC CAG AAT-3′), R2 (5′-TCT GCA CCT CCA CTT CGC TCA-3′ and 5′-TAG GTG GTG GCC TTG GAA GCT-3′), H3 (5′-AGC GAA GAG GAG ATG GCC CGT-3′ and 5′-AGG AGC TCC GTG CTC TTC TGG T-3′), CDKA;1 (5′-ATC ACG GCA ACA TCG TCA GG-3′ and 5′-AGT AAG CAA CGC CGC GGA GTA-3′), CDKA;2 (5′-ACC ACC GCA TAG TCA AAT CGT T-3′ and 5′-ACC ACA ATG TCA CCA CCT CGT GA-3′), XTR1 (5′-AGC CGT ACA TCC TGC AGA CGA-3′ and 5′-GCC CAG GTC CTT GCT GTT CT-3′), CPD1 (5′-TCT TCT CCA TCC CCT TTC CTC T-3′ and 5′-TCA AGA AGC TCC TCA ACC ATG T-3′ [44]), DWF4 (5′-AGT CGC GTG CTG CCA TTC T-3′ and 5′-AGC TCA GCA AGA GGT CCA GGA T-3′ [3]), BRI1 (5′-TAC CAG AGC TTC AGA TGC ACC A-3′ and 5′-AGT AGC TCA GGG TCG AAG ACA T-3′ [13]), OsGA2ox3 (5′-TTC TTC GTC AAC GTC GGC GAC TCG TTG C-3′ and 5′-TCT CAA ACT GGG CCA GCC TGT TGT CTC C-3′ [39]), OsGA20ox2 (5′-TAC TAC AGG GAG TTC TTC GCG GAC AGC A-3′ and 5′-TGT GCA GGC AGC TCT TAT ACC TCC CGT T-3′ [39]), OsIAA1 (5′-GCC GCT CAA TGA GGC ATT-3′ and 5′-GCT TCC ACT TTC TTT CAA TCC AA-3′ [40]), OsIAA9 (5′-AAG AAA ATG GCC AAT GAT GAT CA-3′ and 5′-CCC ATC ACC ATC CTC GTA GGT-3′ [40]), and OsIAA24 (5′-GGC TTG TGC TCT TCG TTG CT-3′ and 5′-CCT CTT GGA TTC AGA AAC ACT GAA-3′ [40]). …”

Antagonistic HLH/bHLH Transcription Factors Mediate Brassinosteroid Regulation of Cell Elongation and Plant Development in Rice andArabidopsis

“…In addition, BR regulates multiple developmental and physiological processes, such as vascular differentiation, reproductive development, photomorphogenesis, and stress responses (Clouse and Sasse, 1998;Bishop and Koncz, 2002;Fukuda, 2004). BR-deficient and BR-insensitive mutant plants show dwarfism, dark-green leaves, male sterility, and constitutive photomorphogenesis in the dark (Chory et al, 1991;Szekeres et al, 1996;Li and Chory, 1997;Mori et al, 2002).…”

Signaling and gene regulatory programs in plant vascular stem cells

“…The role of BRs in vascular development was supported by phenotypes of BR signaling mutants in Arabidopsis, rice, and Zinnia (Cano-Delgado et al, 2010; Mori et al, 2002). The BR deficient mutant, constitutive photomorphogenic dwarf (cpd) was first identified to be defective in BR biosynthesis and has exhibited severe decline in xylem biogenesis (Szekeres et al, 1996).…”