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


CONCLUSIONS
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.
Department of Chemistry, Seoul National University, Seoul, 151-742, South Korea. eyjeong@snu.ac.kr.
Eun-Young
EY
Jeong
Department of Chemistry, Seoul National University, Seoul, 151-742, South Korea. pjseo1@jbnu.ac.kr.
Pil Joon
PJ
Seo
Department of Biological Science, Mokpo National University, Jeonnam, 534-729, South Korea. jcwoo@mokpo.ac.kr.
Je Chang
JC
Woo
Department of Chemistry, Seoul National University, Seoul, 151-742, South Korea. cmpark@snu.ac.kr.|Plant Genomics and Breeding Institute, Seoul National University, Seoul, 151-742, South Korea. cmpark@snu.ac.kr.
Chung-Mo
CM
Park
D017360:Arabidopsis / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D035264:Flowers; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation
D029681:Arabidopsis Proteins; D017346:Protein Serine-Threonine Kinases; D014157:Transcription Factors; C531469:At3g01090 protein, Arabidopsis