688 / 2019-05-01 10:39:20

Arabidopsis SPA2 Represses Seedling De-etiolation in Darkness and under All Light Conditions

Arabidopsis, photomorphogenesis, SPA2, COP1, phyA, phyB, and cry1

Growth and Development > Growth and Development

SPA (SUPPRESSOR OF PHYA-105) gene family (SPA1-SPA4) forms E3 ubiquitin ligase complexs with CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), which is responsible for the degradation of various photomorphogenesis promoting factors, such as HY5, HFR1, and LAF1, resulting in desensitization to light signaling. It has been reported that SPA2 promotes skotomorphogenesis in darkness. However, the unique roles of SPA2 in suppressing photomorphogenesis under light conditions are largely unknown. Here, found that SPA2 functions redundantly with SPA1 in multiple light conditions as well as in darkness. The spa2–100 mutant enhances the seedling de-etiolation phenotype conferred by the spa1–100 mutant in the dark or under weak far-red (FR), red (R), blue (B) and white (W) light-conditions. Similar to SPA1, overexpression of Myc–SPA2 and Myc–SPA2–CT472 results in hyper-etiloation phenotype under various light-conditions. Our findings support that the N-terminal kinase-like domain of SPA2 is necessary for its degradation, and that both the central coiled-coil and the C-terminal WD40-repeat domains are sufficient in repressing light signaling, including seedling de-etiolaton, cotyledon unfolding and hypocotyl negative geotropism. Notably, phyA, phyB, and cry1 interact with SPA2 in vitro and in vivo, and they suppress SPA2 protein accumulations and activities under FR, R, or B light, respectively. Furthermore, we confirm COP1 was involved in the control of the accumulation or stability of SPA2.