REVERSAL OF RDO5 1, a Homolog of Rice Seed Dormancy4, Interacts with bHLH57 and Controls ABA Biosynthesis and Seed Dormancy in Arabidopsis

Abstract

Short title: ODR1 Interacts with bHLH57 and Controls Seed Dormancy One-sentence summary: ODR1 negatively controls seed dormancy by interacting with the transcription factor bHLH57 and preventing its induction of NCED6 and NCED9 expression and ABA biosynthesis.

ABA Metabolism and Homeostasis in Seed Dormancy and Germination

“…ABI3 is a central transcription factor in the ABA signaling network and, in contrast to other lafl , Arabidopsis abi3 mutants have been identified by their germination insensitivity to ABA [ 90 ]. ABI3 has been recently reported to bind to the promoter and repress the expression of REVERSAL of RDO5 1 gene ( ODR1 ) and ODR1 to act as a regulator of ABA biosynthesis [ 91 ]. DELAY OF GERMINATION18 ( DOG18 )/ REDUCED DORMANCY 5 ( RDO5 ) was previously identified by both mutant screen and QTL analysis for low dormancy.…”

“…In Arabidopsis, ODR1 was shown to interact with bHLH57, a basic helix-loop-helix transcription factor, which binds to NCED6 and NCED9 promoters and activates gene expression ( Figure 3 ). ODR1 protein itself cannot directly bind to NCED promoters, but its interaction with bHLH57 in a complex negatively impacts on NCED gene transcription and consequently on dormancy induction [ 91 ]. In contrast to ODR1, the expression of the rice Sdr4 protein is positively regulated by OsVP1, the rice ortholog of ABI3, and in accordance positively affects dormancy in several rice cultivars [ 93 ].…”

“…The opposite effects of ODR1 and Sdr4 on seed dormancy may result from their differential regulation by either ABI3 or VP1 and also from differences in expression of Arabidopsis and rice DOG1 homologs, DOG1 being upregulated in odr1 and downregulated in sdr4 . The regulation of ABA metabolism by rice Sdr4 still remains to be studied [ 91 ]. Together with DOG1 , expression of the genes encoding ABI4 and the Drought Response Element binding protein DREB2C is increased in odr1 dry and hydrated seeds, compared to wild-type, however no direct protein interaction with ODR1 has been observed.…”

“…Together with DOG1 , expression of the genes encoding ABI4 and the Drought Response Element binding protein DREB2C is increased in odr1 dry and hydrated seeds, compared to wild-type, however no direct protein interaction with ODR1 has been observed. Since DREB2C and ABI4 transcription factors have been previously shown to interact with NCED6 and NCED9 promoters, ODR1 has been hypothesized to act not only through direct interaction with bHLH57, but also indirectly by downregulating the expression of ABI4 and DREB2C [ 91 , 94 , 95 ].…”

“…A number of other regulators upstream of ABI and SOMNUS have been described [ 5 ], which could have a downstream effect on ABA accumulation and gene expression. Furthermore, ODR1 which functions downstream of ABI3 in seed dormancy regulation [ 91 ] may possibly have a role in germination responses to exogenous signals.…”