Karrikins enhance light responses during germination and seedling development in Arabidopsis thaliana

Abstract

Karrikins are a class of seed germination stimulants identified in smoke from wildfires. Microarray analysis of imbibed Arabidopsis thaliana seeds was performed to identify transcriptional responses to KAR 1 before germination. A small set of genes that are regulated by KAR 1 , even when germination is prevented by the absence of gibberellin biosynthesis or light, were identified. Light-induced genes, putative HY5-binding targets, and ABRE-like promoter motifs were overrepresented among KAR 1 -up-regulated genes. KAR 1 transiently induced the light signal transduction transcription factor genes HY5 and HYH. Germination of afterripened Arabidopsis seed was triggered at lower fluences of red light when treated with KAR 1 . Light-dependent cotyledon expansion and inhibition of hypocotyl elongation were enhanced in the presence of germination-active karrikins. HY5 is important for the Arabidopsis hypocotyl elongation, but not seed germination, response to karrikins. These results reveal a role for karrikins in priming light responses in the emerging seedling, and suggest that the influence of karrikins on postfire ecology may not be limited to germination recruitment.smoke | photomorphogenesis

Burning vegetation produces cyanohydrins that liberate cyanide and stimulate seed germination

“…1a) 11 , which was recently named karrikinolide (or KAR 1 ) after the Aboriginal Noongar word for smoke, karrik 12 . Smoke-responsive seeds of a large number of species respond to karrikinolide, demonstrating that it is a major contributor to the germination activity of smoke and an ecologically significant germination cue [13][14][15] .…”

Smoke-derived karrikin perception by the α/β-hydrolase KAI2 from Arabidopsis

“…Germination-stimulating compounds, generated in the smoke of burning plants, include a seed dormancybreaking compound 3-methyl-2H-furo [2,3-c]pyran-2-one, a butenolide named karrikinolide-1 or karrikin-1 (KAR 1 ) (2). Previous reports reveal KAR 1 structure-activity relationships (SARs) and features of the physiological mode of action (3)(4)(5)(6)(7). Karrikinsinsensitive (kai) mutants in the model plant Arabidopsis thaliana identify some of the genetic components underlying karrikins' perception and signaling (8,9).…”

From little things big things grow: karrikins and new directions in plant development

“…In epigeal seedlings like Arabidopsiswhere the cotyledons emerge above ground and become photosynthetic -photomorphogenesis is characterised by greening and expansion of the cotyledons, reduction or cessation of hypocotyl elongation, and increased root growth relative to dark-grown seedlings. Treatment of wild-type Arabidopsis seedlings with 100 nM KAR 1 or KAR 2 led to an enhancement of these traits, especially cotyledon expansion and inhibition of hypocotyl elongation (Nelson et al 2010). As with seed germination, Arabidopsis seedlings were more responsive to KAR 2 than to KAR 1 .…”

“…As with seed germination, Arabidopsis seedlings were more responsive to KAR 2 than to KAR 1 . Karrikins also reduced the minimum amount of red light required to trigger germination after an inhibitory far-red light pulse; however, karrikins were insufficient to overcome the requirement for light altogether, suggesting that they act downstream of phytochrome B in the control of germination and photomorphogenesis (Nelson et al 2010). Nevertheless, karrikins do induce transcriptional changes in darkness, suggesting that some karrikin responses are lightindependent .…”