The Oryza sativa Regulator HDR1 Associates with the Kinase OsK4 to Control Photoperiodic Flowering

Abstract

Rice is a facultative short-day plant (SDP), and the regulatory pathways for flowering time are conserved, but functionally modified, in Arabidopsis and rice. Heading date 1 (Hd1), an ortholog of Arabidopsis CONSTANS (CO), is a key regulator that suppresses flowering under long-day conditions (LDs), but promotes flowering under short-day conditions (SDs) by influencing the expression of the florigen gene Heading date 3a (Hd3a). Another key regulator, Early heading date 1 (Ehd1), is an evolutionarily unique gene with no orthologs in Arabidopsis, which acts as a flowering activator under both SD and LD by promoting the rice florigen genes Hd3a and RICE FLOWERING LOCUST 1 (RFT1). Here, we report the isolation and characterization of the flowering regulator Heading Date Repressor1 (HDR1) in rice. The hdr1 mutant exhibits an early flowering phenotype under natural LD in a paddy field in Beijing, China (39°54'N, 116°23'E), as well as under LD but not SD in a growth chamber, indicating that HDR1 may functionally regulate flowering time via the photoperiod-dependent pathway. HDR1 encodes a nuclear protein that is most active in leaves and floral organs and exhibits a typical diurnal expression pattern. We determined that HDR1 is a novel suppressor of flowering that upregulates Hd1 and downregulates Ehd1, leading to the downregulation of Hd3a and RFT1 under LDs. We have further identified an HDR1-interacting kinase, OsK4, another suppressor of rice flowering under LDs. OsK4 acts similarly to HDR1, suppressing flowering by upregulating Hd1 and downregulating Ehd1 under LDs, and OsK4 can phosphorylate HD1 with HDR1 presents. These results collectively reveal the transcriptional regulators of Hd1 for the day-length-dependent control of flowering time in rice.

Expression of sugarcane genes associated with perception of photoperiod and floral induction reveals cycling over a 24-hour period

“…The expression profile of ShFT-A, over a 24-h cycle, was similar to FT profiles reported in rice (known as Hd3A and RFT1; Komiya et al 2008;Zhao et al 2012;Wang et al 2013;Lee and An 2015) and sorghum (known as CENTRORADIALES, CN; Yang et al 2014). In rice the expression peak of Hd3a and RFT1 was at the transition from dark to light in both photoperiod inductive and non-inductive conditions, however there was a higher level of expression under the inductive conditions (Izawa et al 2002;Lee et al 2016;Sun et al 2016). This expression profile for ShFT-A is an important base line to assess changes in expression during floral induction.…”

Alternative functions of Hd1 in repressing or promoting heading are determined by Ghd7 status under long-day conditions

“…However, recent studies have shown that Hd1 represses the expression of Ehd1 in LD 33 , 34 , suggesting that Hd1 - and Ehd1 -mediated pathways are not always independent. In a recent report, Heading Date Repressor 1 (HDR1) and OsK4 were found to suppress heading date by upregulating Hd1 and downregulating Ehd1 , and the HDR1-OsK4 interaction complex can phosphorylate Hd1 35 .…”

Transcriptomic and Targeted Metabolomic Analysis Identifies Genes Controlling for Early Bolting and Flowering in Angelica Sinensis

“…MIP1A and MIP1B that repress owering by forming heterodimeric complexes that sequester CO and COL proteins into non-functional complexes [26] were also found to be up-regulated in BP. Another inconsistent transcriptional response for owering is up regulation of HEADING DATE REPRESSOR 1 (HDR1), a owering suppressor that up-regulates HD1 in LD conditions [61]. Again, inconsistent regulation of photoperiod pathway transcripts associated with owering in BP suggests down-stream signaling involvement in early bolting.…”