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AKIN10 delays flowering by inactivating IDD8 transcription factor through protein phosphorylation in Arabidopsis.

Jeong EY, Seo PJ, Woo JC, Park CM - BMC Plant Biol. (2015)

Bottom Line: We found that AKIN10 interacts with IDD8 in the nucleus.AKIN10-mediated phosphorylation did not affect the subcellular localization and DNA-binding property of IDD8.Instead, the transcriptional activation activity of the phosphorylated IDD8 was significantly reduced.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Seoul National University, Seoul, 151-742, South Korea. eyjeong@snu.ac.kr.

ABSTRACT

Background: Sugar plays a central role as a source of carbon metabolism and energy production and a signaling molecule in diverse growth and developmental processes and environmental adaptation in plants. It is known that sugar metabolism and allocation between different physiological functions is intimately associated with flowering transition in many plant species. The INDETERMINATE DOMAIN (IDD)-containing transcription factor IDD8 regulates flowering time by modulating sugar metabolism and transport under sugar-limiting conditions in Arabidopsis. Meanwhile, it has been reported that SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE 1 (SnRK1), which acts as a sensor of cellular energy metabolism, is activated by sugar deprivation. Notably, SnRK1-overexpressing plants and IDD8-deficient mutants exhibit similar phenotypes, including delayed flowering, suggesting that SnRK1 is involved in the IDD8-mediated metabolic control of flowering.

Results: We examined whether the sugar deprivation-sensing SnRK1 is functionally associated with IDD8 in flowering time control through biochemical and molecular genetic approaches. Overproduction of AKIN10, the catalytic subunit of SnRK1, delayed flowering in Arabidopsis, as was observed in IDD8-deficient idd8-3 mutant. We found that AKIN10 interacts with IDD8 in the nucleus. Consequently, AKIN10 phosphorylates IDD8 primarily at two serine (Ser) residues, Ser-178 and Ser-182, which reside in the fourth zinc finger (ZF) domain that mediates DNA binding and protein-protein interactions. AKIN10-mediated phosphorylation did not affect the subcellular localization and DNA-binding property of IDD8. Instead, the transcriptional activation activity of the phosphorylated IDD8 was significantly reduced. Together, these observations indicate that AKIN10 antagonizes the IDD8 function in flowering time control, a notion that is consistent with the delayed flowering phenotypes of AKIN10-overexpressing plants and idd8-3 mutant.

Conclusion: Our data show that SnRK1 and its substrate IDD8 constitute a sugar metabolic pathway that mediates the timing of flowering under sugar deprivation conditions. In this signaling scheme, the SnRK1 signals are directly integrated into the IDD8-mediated gene regulatory network that governs flowering transition in response to fluctuations in sugar metabolism, further supporting the metabolic control of flowering.

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AKIN10 overexpression delays flowering. Plants were grown in soil under LDs for 6 weeks before taking photographs (A). Flowering times were measured by counting the days to bolting and rosette leaf numbers at bolting (B, left and right panels, respectively). Transgenic plants overexpressing IDD8 (8-ox1 and 8-ox2), AKIN10 (10-ox), and AKIN11 (11-ox) and their gene knockout mutants were analyzed. The countings of approximately 20 plants were averaged and statistically analyzed using Student t-test (*P < 0.01, difference from col-0). Bars indicate standard error of the mean.
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Fig1: AKIN10 overexpression delays flowering. Plants were grown in soil under LDs for 6 weeks before taking photographs (A). Flowering times were measured by counting the days to bolting and rosette leaf numbers at bolting (B, left and right panels, respectively). Transgenic plants overexpressing IDD8 (8-ox1 and 8-ox2), AKIN10 (10-ox), and AKIN11 (11-ox) and their gene knockout mutants were analyzed. The countings of approximately 20 plants were averaged and statistically analyzed using Student t-test (*P < 0.01, difference from col-0). Bars indicate standard error of the mean.

Mentions: We examined the flowering phenotypes of the plants grown under long days (LDs, 16-h light and 8-h dark) by counting the numbers of rosette leaves at bolting and the days to bolting. The 8-ox plants and the akin10-1 and akin11-1 mutants did not exhibit any discernible flowering phenotypes under our assay conditions (Figures 1A and 1B). In contrast, the 10-ox and 11-ox plants exhibited delayed flowering, as observed in idd8-3 mutant. The delay of flowering time was more prominent in 10-ox than in 11-ox (Figure 1B). The similar flowering phenotypes raised a possibility that loss of IDD8 function is related with overproduction of AKIN10 and AKIN11 in regulating flowering time. In support of this hypothesis, the expression of SUS4 and SUC genes was suppressed in the 10-ox plants but up-regulated in the akin10-1 mutant (Additional file 3), as observed in the idd8-3 mutant and the 8-ox plants, respectively [20].Figure 1


AKIN10 delays flowering by inactivating IDD8 transcription factor through protein phosphorylation in Arabidopsis.

Jeong EY, Seo PJ, Woo JC, Park CM - BMC Plant Biol. (2015)

AKIN10 overexpression delays flowering. Plants were grown in soil under LDs for 6 weeks before taking photographs (A). Flowering times were measured by counting the days to bolting and rosette leaf numbers at bolting (B, left and right panels, respectively). Transgenic plants overexpressing IDD8 (8-ox1 and 8-ox2), AKIN10 (10-ox), and AKIN11 (11-ox) and their gene knockout mutants were analyzed. The countings of approximately 20 plants were averaged and statistically analyzed using Student t-test (*P < 0.01, difference from col-0). Bars indicate standard error of the mean.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4416337&req=5

Fig1: AKIN10 overexpression delays flowering. Plants were grown in soil under LDs for 6 weeks before taking photographs (A). Flowering times were measured by counting the days to bolting and rosette leaf numbers at bolting (B, left and right panels, respectively). Transgenic plants overexpressing IDD8 (8-ox1 and 8-ox2), AKIN10 (10-ox), and AKIN11 (11-ox) and their gene knockout mutants were analyzed. The countings of approximately 20 plants were averaged and statistically analyzed using Student t-test (*P < 0.01, difference from col-0). Bars indicate standard error of the mean.
Mentions: We examined the flowering phenotypes of the plants grown under long days (LDs, 16-h light and 8-h dark) by counting the numbers of rosette leaves at bolting and the days to bolting. The 8-ox plants and the akin10-1 and akin11-1 mutants did not exhibit any discernible flowering phenotypes under our assay conditions (Figures 1A and 1B). In contrast, the 10-ox and 11-ox plants exhibited delayed flowering, as observed in idd8-3 mutant. The delay of flowering time was more prominent in 10-ox than in 11-ox (Figure 1B). The similar flowering phenotypes raised a possibility that loss of IDD8 function is related with overproduction of AKIN10 and AKIN11 in regulating flowering time. In support of this hypothesis, the expression of SUS4 and SUC genes was suppressed in the 10-ox plants but up-regulated in the akin10-1 mutant (Additional file 3), as observed in the idd8-3 mutant and the 8-ox plants, respectively [20].Figure 1

Bottom Line: We found that AKIN10 interacts with IDD8 in the nucleus.AKIN10-mediated phosphorylation did not affect the subcellular localization and DNA-binding property of IDD8.Instead, the transcriptional activation activity of the phosphorylated IDD8 was significantly reduced.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Seoul National University, Seoul, 151-742, South Korea. eyjeong@snu.ac.kr.

ABSTRACT

Background: Sugar plays a central role as a source of carbon metabolism and energy production and a signaling molecule in diverse growth and developmental processes and environmental adaptation in plants. It is known that sugar metabolism and allocation between different physiological functions is intimately associated with flowering transition in many plant species. The INDETERMINATE DOMAIN (IDD)-containing transcription factor IDD8 regulates flowering time by modulating sugar metabolism and transport under sugar-limiting conditions in Arabidopsis. Meanwhile, it has been reported that SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE 1 (SnRK1), which acts as a sensor of cellular energy metabolism, is activated by sugar deprivation. Notably, SnRK1-overexpressing plants and IDD8-deficient mutants exhibit similar phenotypes, including delayed flowering, suggesting that SnRK1 is involved in the IDD8-mediated metabolic control of flowering.

Results: We examined whether the sugar deprivation-sensing SnRK1 is functionally associated with IDD8 in flowering time control through biochemical and molecular genetic approaches. Overproduction of AKIN10, the catalytic subunit of SnRK1, delayed flowering in Arabidopsis, as was observed in IDD8-deficient idd8-3 mutant. We found that AKIN10 interacts with IDD8 in the nucleus. Consequently, AKIN10 phosphorylates IDD8 primarily at two serine (Ser) residues, Ser-178 and Ser-182, which reside in the fourth zinc finger (ZF) domain that mediates DNA binding and protein-protein interactions. AKIN10-mediated phosphorylation did not affect the subcellular localization and DNA-binding property of IDD8. Instead, the transcriptional activation activity of the phosphorylated IDD8 was significantly reduced. Together, these observations indicate that AKIN10 antagonizes the IDD8 function in flowering time control, a notion that is consistent with the delayed flowering phenotypes of AKIN10-overexpressing plants and idd8-3 mutant.

Conclusion: Our data show that SnRK1 and its substrate IDD8 constitute a sugar metabolic pathway that mediates the timing of flowering under sugar deprivation conditions. In this signaling scheme, the SnRK1 signals are directly integrated into the IDD8-mediated gene regulatory network that governs flowering transition in response to fluctuations in sugar metabolism, further supporting the metabolic control of flowering.

Show MeSH
Related in: MedlinePlus