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 ( GA ) 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 .
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