Genetic Background Influences Brassinosteroid-Related Mutant Phenotypes in Rice

Abstract

In two cases, mutations in the same brassinosteroid-related genes caused different phenotypes in japonica varieties Nipponbare and Taichung 65. The mutant phenotypes were less severe in the Taichung 65 background than in the Nipponbare background. Three newly isolated brassinosteroid-insensitive mutants (d61-1N, d61-11, and d61-12) derived from a Nipponbare mutant library were found to be alleles of d61, which represent defects in the OsBRI1 gene. Although the Nipponbare-derived mutant d61-1N had the same nucleotide substitution as the previously characterized Taichung 65-derived mutant d61-1T, these two mutants showed different phenotypes for plant stature, internode elongation pattern, and seed shape; in each case, d61-1N (in the Nipponbare genetic background) had the more severe mutant phenotype. Similar trends were seen for phenotypes caused by mutants of d2, a brassinosteroid biosynthesis gene. Consistent with these phenotypes, the expression of brassinosteroid-responsive genes was lower in the Nipponbare-derived mutants. These results can be explained by our findings that feed-forward up-regulation of OsBRI1 did not occur in the Nipponbare-derived mutants and that an mPing transposon is inserted into the promoter region of Nipponbare OsBRI1. Based on these results, we conclude that the expression of OsBRI1, especially its feed-forward up-regulation, is misregulated in wild-type Nipponbare and in brassinosteroid-related mutants in a Nipponbare genetic background. Although Nipponbare is a model rice genotype, it can be categorized as an OsBRI1 mutant that has reduced sensitivity to brassinosteroid.

Association mapping of brassinosteroid candidate genes and plant architecture in a diverse panel of Sorghum bicolor

“…No mutants have been reported for BKI1 and BSK1 in rice but, proteins from both genes interact with BRI1, and BRI1 mutants have been extensively characterized in this species. Sakamoto et al (2013) identified three OsBRI1 mutants (d61-1 N, d61-11, and d61-12) which showed variation in plant height, leaf angle, internode elongation, and seed shape. Mutant phenotypes included shorter plants, reduced leaf angle, abnormal and twisted leaves, reduced internode elongation and plants without flowers (Sakamoto et al 2013).…”

“…Sakamoto et al (2013) identified three OsBRI1 mutants (d61-1 N, d61-11, and d61-12) which showed variation in plant height, leaf angle, internode elongation, and seed shape. Mutant phenotypes included shorter plants, reduced leaf angle, abnormal and twisted leaves, reduced internode elongation and plants without flowers (Sakamoto et al 2013). Since proteins translated from BSK1 and BKI1 genes interact directly with BRI1, we can speculate that similar effects on the phenotype could be observed by allelic variations in BSK1 and BKI1, as shown in our study.…”

Rice ERECT LEAF 1 acts in an alternative brassinosteroid signaling pathway independent of the receptor kinase OsBRI1

“…d61-12 is a leaky mutant that caused by a single amino acid substitution in the leucine-rich repeats of OsBRI1. 29 Althouth brd1-5 was indistinguishable from elf1-1/d61-1 double mutant (Fig. 1A, B), d61-12 showed similar phenotypes to those of elf1-1 single mutant such as severe dwarf phenotype with erect leaves and small grains.…”

“…We have previously identified 12 alleles of d61 mutants, which have phenotypes of varying severity caused by defects in OsBRI1 function. 29 One of them, d61-12, was morphologically very similar to elf1-1; therefore, we chose d61-12 for microarray analysis to eliminate any indirect effects of morphological alterations. As expected from the elf1-1/d61-1 phenotype, the expression profile of elf1-1 was distinct from that of d61-12, and fewer than half of the genes differentially expressed between elf1-1 and the wild-type showed similar changes in d61-12 relative to the wild-type.…”

An E3 ubiquitin ligase, ERECT LEAF1, functions in brassinosteroid signaling of rice

“…11 Although the first 2 d61 mutants identified were weak alleles, 12 alleles with different severities of phenotype have been identified to date. 12,13 Two other brassinosteroid-insensitive rice mutants, dlt and lic, have also been identified. 14,15 DLT encodes a GRASfamily transcription factor and probably acts downstream of a putative rice BZR1 ortholog.…”