Identification of a new gene controlling plant height in rice using the candidate-gene strategy.

A gene underlying a quantitative trait locus (QTL) controlling plant height on chromosome 1 (QTLph1) in rice ( Oryza sativa L.) was identified using the candidate-gene strategy. First, the function of a targeted gene was analyzed using near isogenic lines (NILs) in which the chromosomal region of a targeted QTL was substituted with that of another line. Second, for physiological information, the candidate gene was selected in the annotation data by the genome sequencing. Physiological analyses of an NIL-expressing QTLph1 (NIL6) suggested that the targeted gene controls plant height by enabling higher amounts of sucrose to be translocated in leaves. The results indicated that the gene for sucrose phosphate synthase (SPS; EC 2.4.1.14), the major limiting enzyme for sucrose synthesis, is a candidate gene for QTLph1 among the annotation results of the region of QTLph1. The higher level of SPS transcripts and the activity of SPS in NIL6 compared to control plants, and the fact that the relative SPS activity per SPS protein content was almost the same between NIL6 and Nipponbare suggested that the higher plant height in NIL6 compared to Nipponbare was due to the high SPS activity in NIL6. In agreement with this hypothesis, transgenic rice plants with a maize SPS gene that had about 3 times the SPS activity of that in Nipponbare (control plants) were significantly taller than Nipponbare from the early growth stage. From these results and the physiological data from NIL6, we concluded that SPS is the targeted gene underlying QTLph1.