Abstract
Circadian clock coordinates numerous plant growth and developmental processes including cell elongation in the hypocotyl, whether or not it modulates cell proliferation is largely unknown. Here we have found that Pseudo Response Regulators (PRRs), essential components of circadian core oscillators, affect root meristem cell proliferation mediated by Target Of Rapamycin (TOR) signaling. The null mutants of PRRs display much reduced sensitivities to sugar-activated TOR signaling. We have subsequently identified Tandem Zinc Finger 1, encoding a processing body localized RNA-binding protein, as a direct target repressed by PRRs in mediating TOR signaling. Multiple lines of biochemical and genetic evidence have demonstrated that TZF1 acts downstream of PRRs to attenuate TOR signaling. Furthermore, TZF1 could directly bind TOR mRNA via its tandem zinc finger motif to affect TOR mRNA stability. Our findings support a notion that PRR-TZF1-TOR molecular axis modulates root meristem cell proliferation by integrating both transcriptional and post-transcriptional regulatory mechanisms.
Highlights
Circadian clocks are ubiquitous biochemical time-keeping machineries that consist of non-orthologous interlocking feedback loops in distinct organisms [1]
PRR5, PRR7 and PRR9 appeared to redundantly affect Glc-Target Of Rapamycin (TOR) signaling, as the corresponding single mutants were all less sensitive to Glc-TOR signaling compared with Col-0 (Supplementary Figure S2)
We have found that the Pseudo Response Regulators (PRRs) proteins modulate GlcTOR signaling-mediated root meristem cell proliferation
Summary
Circadian clocks are ubiquitous biochemical time-keeping machineries that consist of non-orthologous interlocking feedback loops in distinct organisms [1]. Besides the essential roles within core oscillators, PRR5, PRR7, together with PRR9 play pivotal roles in coordinating many daily cycling physiological processes by timing the expression of numerous downstream transcription factors, such as those involved in oxidative stress response and stomata opening [4,5]. The high chlorophyll contents and elevated glucose accumulation at dawn in prr, prr and prr resemble that in a glucose sensor (Hexokinase 1, HXK1) mutant glucose insensitive 2 (gin2) [8], raising a possibility that PRR proteins are closely involved in sugar signaling. Given there is a close connection between circadian clock and TOR signaling in mammals [10,11,12], it is conceivable that PRR proteins might mediate this much-needed crosstalk in higher plants
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