Brassinosteroids regulate grain filling in rice.
Genes controlling hormone levels have been used to increase grain yields in wheat (Triticum aestivum) and rice (Oryza sativa). We created transgenic rice plants expressing maize (Zea mays), rice, or Arabidopsis thaliana genes encoding sterol C-22 hydroxylases that control brassinosteroid (BR) hormone levels using a promoter that is active in only the stems, leaves, and roots. The transgenic plants produced more tillers and more seed than wild-type plants. The seed were heavier as well, especially the seed at the bases of the spikes that fill the least. These phenotypic changes brought about 15 to 44% increases in grain yield per plant relative to wild-type plants in greenhouse and field trials. Expression of the Arabidopsis C-22 hydroxylase in the embryos or endosperms themselves had no apparent effect on seed weight. These results suggested that BRs stimulate the flow of assimilate from the source to the sink. Microarray and photosynthesis analysis of transgenic plants revealed evidence of enhanced CO(2) assimilation, enlarged glucose pools in the flag leaves, and increased assimilation of glucose to starch in the seed. These results further suggested that BRs stimulate the flow of assimilate. Plants have not been bred directly for seed filling traits, suggesting that genes that control seed filling could be used to further increase grain yield in crop plants.
Wu
Chuan-yin
CY
Ceres Inc., Thousand Oaks, California 91320, USA.
Trieu
Anthony
A
Radhakrishnan
Parthiban
P
Kwok
Shing F
SF
Harris
Sam
S
Zhang
Ke
K
Wang
Jiulin
J
Wan
Jianmin
J
Zhai
Huqu
H
Takatsuto
Suguru
S
Matsumoto
Shogo
S
Fujioka
Shozo
S
Feldmann
Kenneth A
KA
Pennell
Roger I
RI
D018506:Gene Expression Regulation, Plant; D020411:Oligonucleotide Array Sequence Analysis; D012275:Oryza / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013260:Steroids, Heterocyclic / Q000378:metabolism*
D013260:Steroids, Heterocyclic