Abstract
The kinesins are a family of microtubule-based motor proteins that move directionally along microtubules and are involved in many crucial cellular processes, including cell elongation in plants. Less is known about kinesins directly regulating gene transcription to affect cellular physiological processes. Here, we describe a rice (Oryza sativa) mutant, gibberellin-deficient dwarf1 (gdd1), that has a phenotype of greatly reduced length of root, stems, spikes, and seeds. This reduced length is due to decreased cell elongation and can be rescued by exogenous gibberellic acid (GA₃) treatment. GDD1 was cloned by a map-based approach, was expressed constitutively, and was found to encode the kinesin-like protein BRITTLE CULM12 (BC12). Microtubule cosedimentation assays revealed that BC12/GDD1 bound to microtubules in an ATP-dependent manner. Whole-genome microarray analysis revealed the expression of ent-kaurene oxidase (KO2), which encodes an enzyme involved in GA biosynthesis, was downregulated in gdd1. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed that GDD1 bound to the element ACCAACTTGAA in the KO2 promoter. In addition, GDD1 was shown to have transactivation activity. The level of endogenous GAs was reduced in gdd1, and the reorganization of cortical microtubules was altered. Therefore, BC12/GDD1, a kinesin-like protein with transcription regulation activity, mediates cell elongation by regulating the GA biosynthesis pathway in rice.
Highlights
The yield of crops, including rice (Oryza sativa), is a concern around the world
The mutant, designated gibberellin-deficient dwarf1, retained a stable phenotype and showed segregation of the b-glucuronidase (GUS) gene with the T-DNA insertions until T2 progeny, suggesting that the phenotype was independent of the T-DNA insertion, the mutant with neither the T-DNA insertion nor GUS fragment from the T2 progeny was used for analysis the function of GDD1
Phylogenetic analysis and MT binding assay revealed that GDD1/BRITTLE CULM12 (BC12) belongs to the KIF4 kinesin protein family
Summary
The yield of crops, including rice (Oryza sativa), is a concern around the world. Dwarf plants with high yield potential, for the Green Revolution, are an attractive phenotype for crop breeding. More than 60 rice dwarf mutants have been found (Matsuo et al, 1997). One of the GA 20-oxidase (GA20ox) genes in rice, GA20ox (SD1), is a well-known gene studied in Green Revolution rice varieties (Sasaki et al, 2002). GIBBERELLIN INSENSITIVE DWARF1 (GID1) in rice encodes a soluble receptor that mediates GA signaling (Ueguchi-Tanaka et al, 2005). GID2 encodes an F-box protein important in protein degradation (Sasaki et al, 2003).
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