Tomoyuki Furuta, Norio Komeda, Kenji Asano, Kanako Uehara, Rico Gamuyao, Rosalyn B. Angeles-Shim, Keisuke Nagai, Kazuyuki Doi, Diane R. Wang, Hideshi Yasui, Atsushi Yoshimura, Jianzhong Wu, Susan R. McCouch and Motoyuki Ashikari

G3 November 1, 2015 vol. 5 no. 11 2267-2274 (Genes, Genomes, Genetics)

Abstract

A long awn is one of the distinct morphological features of wild rice species. This organ is thought to aid in seed dispersal and prevent predation by animals. Most cultivated varieties of Oryza sativa and Oryza glaberrima, however, have lost the ability to form long awns. The causal genetic factors responsible for the loss of awn in these two rice species remain largely unknown. Here, we evaluated three sets of chromosome segment substitution lines (CSSLs) in a common O. sativa genetic background (cv. Koshihikari) that harbor genomic fragments from Oryza nivara, Oryza rufipogon, and Oryza glaberrima donors. Phenotypic analyses of these libraries revealed the existence of three genes, Regulator of Awn Elongation 1 (RAE1), RAE2, and RAE3, involved in the loss of long awns in cultivated rice. Donor segments at two of these genes, RAE1 and RAE2, induced long awn formation in the CSSLs whereas an O. sativa segment at RAE3 induced long awan formation in O. glaberrima. These results suggest that the two cultivated rice species, O. sativa and O. glaberrima, have taken independent paths to become awnless.

Figure 3

Positional cloning, complementation, and expression analysis of RAE1. (A) RAE1 was mapped at the proximal part of the long arm of chromosome 4. This region has four annotated genes in O. sativa, whereas O. glaberrima only has two (Os04g0350700 and Os04g0351333) of four genes in the corresponding region. (B–G) Complementation test and overexpression analysis were performed using awnless O. sativa cv. Nipponbare. Long awn formations were observed in the transgenic line of Comp.1 harboring the entire genomic fragment of Os04g0350700 derived from O. glaberrima (B), whereas Comp.2 and Comp.3 did not show awn formation (C and D). Overexpression of O. glaberrima allele (Ox_Og) (F) and Koshihikari allele (Ox_Os) (G) of Os04g0350700 induced long awn formations in Nipponbare, whereas vector control showed no awn (E). (H and I) Expression analysis of Os04g0350700 in immature lemma (H) and mature lemma (I) collected from GLSL-13 and Koshihikari. Mean values of three biological replicates are shown. An asterisk indicates the statistical significance at P < 0.01 in Student’s t-test.