Lei Hua, Diane R. Wang, Lubin Tan, Yongcai Fu, Fengxia Liu, Langtao Xiao, Zuofeng Zhu, Qiang Fu, Xianyou Sun, Ping Gu, Hongwei Cai, Susan R. McCouch and Chuanqing Sun

Abstract

Common wild rice (Oryza rufipogon), the wild relative of Asian cultivated rice (Oryza sativa), flaunts long, barbed awns, which are necessary for efficient propagation and dissemination of seeds. By contrast, O. sativa cultivars have been selected to be awnless or to harbor short, barbless awns, which facilitate seed processing and storage. The transition from long, barbed awns to short, barbless awns was a crucial event in rice domestication. Here, we show that the presence of long, barbed awns in wild rice is controlled by a major gene on chromosome 4, LONG AND BARBED AWN1 (LABA1), which encodes a cytokinin-activating enzyme. A frame-shift deletion in LABA1 of cultivated rice reduces the cytokinin concentration in awn primordia, disrupting barb formation and awn elongation. Sequencing analysis demonstrated low nucleotide diversity and a selective sweep encompassing an ∼800-kb region around the derived laba1 allele in cultivated rice. Haplotype analysis revealed that the laba1 allele originated in the japonica subspecies and moved into the indica gene pool via introgression, suggesting that humans selected for this locus in early rice domestication. Identification of LABA1 provides new insights into rice domestication and also sheds light on the molecular mechanism underlying awn development.

See: http://www.plantcell.org/content/27/7/1875.full

PLANT CELL July 2015 vol. 27 no. 7 1875-1888

Figure 1. The Awns of Wild Rice (O. rufipogon) and Cultivated Rice (O. sativa).

(A) Wild rice typically bears a long, barbed awn, which aids in seed dispersal and deters large predators, such as birds. A panicle of wild rice (Tk212) is illustrated in the lower right corner. Bar = 10 cm.

(B) Cultivated rice has either no awns or short and barbless awns and suffers from significant bird predation. A panicle of cultivated rice (93-11, indica) is illustrated in the lower left corner. Bar = 10 cm.

(C) The awn of wild rice (Tk212) is long and barbed. Scanning electron micrograph in the lower right corner shows the surface of the awn of wild rice in the boxed region. Bar = 200 μm.

(D) The awn of cultivated rice (93-11) is short and barbless. Scanning electron micrograph in the lower left corner shows the surface of the awn of cultivated rice in the boxed region. Bar = 200 μm.