A gene controlling the number of primary rachis branches also controls the vascular bundle formation and hence is responsible to increase the harvest index and grain yield in rice.
The quantitative trait locus controlling the number of primary rachis branches (PRBs) in rice was identified using backcrossed inbred lines of Sasanishiki/Habataki//Sasanishiki///Sasanishiki. The resultant gene was ABERRANT PANICLE ORGANIZATION 1 (APO1). Habataki-genotype segregated reciprocal recombinant lines for the APO1 locus increased both the number of PRB (12-13%) and the number of grains per panicle (9-12%), which increased the grain yield per plant (5-7%). Further recombination dividing this region revealed that different alleles regulated the number of PRB and the number of grains per panicle. The PRB1 allele, which includes the APO1 open reading frame (ORF) and the proximal promoter region, controlled only the number of PRB but not the number of grains per panicle. In contrast, the HI1 allele, which includes only the distal promoter region, increased the grain yield and harvest index in Habataki-genotype plants, nevertheless, the ORF expressed was Sasanishiki type. It also increased the number of large vascular bundles in the peduncle. APO1 expression occurred not only in developing panicles but also in the developing vascular bundle systems. In addition, Habataki plants displayed increased APO1 expression in comparison to Sasanishiki plants. It suggests that APO1 enhances the formation of vascular bundle systems which, consequently, promote carbohydrate translocation to panicles. The HI1 allele is suggested to regulate the amount of APO1 expression, and thereby control the development of vascular bundle systems. These findings may be useful to improve grain yield as well as quality through the improvement of translocation efficiency.
Terao
Tomio
T
Rice Physiology Research Sub-Team, Hokuriku Research Center, National Agricultural Research Center, National Agriculture and Food Research Organization, 1-2-1, Inada, Joetsu, Niigata, 943-0193, Japan. terao@affrc.go.jp
Nagata
Kenji
K
Morino
Kazuko
K
Hirose
Tatsuro
T
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D018556:Crops, Agricultural / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D012275:Oryza / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018514:Plant Structures / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development; D030821:Plants, Genetically Modified; D040641:Quantitative Trait Loci; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D010940:Plant Proteins