Cryptochrome 1b from Sweet Sorghum Regulates Photoperiodic Flowering, Photomorphogenesis, and ABA Response in Transgenic Arabidopsis thaliana

Cryptochromes are blue/UV-A light receptors that mediate various aspects of plant growth and development. Here, we report the function and signal mechanism of cryptochrome 1b (SbCRY1b) from sweet sorghum [Sorghum bicolor (L.) Moench], a typical short-day cereal plant, to explore its potential for genetic improvement of sweet sorghum varieties. SbCRY1b mRNA enrichment showed almost 24-h diurnal rhythms in both short-day (SD) and long-day (LD) conditions. Overexpression of SbCRY1b rescued the late-flowering and the long hypocotyl phenotypes of cry1cry2 double mutant in the transgenic Arabidopsis. SbCRY1b mediated Arabidopsis FT mRNA expression in LD and HY5 protein accumulation in response to blue light. SbCRY1b protein was located in both the nucleus and cytoplasm and was degraded by 26S proteasomes in response to blue light. SbCRY1b interacted, respectively, with Arabidopsis suppressor of PHYA-1051 (AtSPA1), E3 ubiquitin ligase constitutive photomorphogenesis 1 (AtCOP1), and a putative COP1 from sweet sorghum (SbCOP1) instead of SbSPA1 in vitro in a blue light-dependent manner. The observations imply SbCRY1b functions as a major regulator of photoperiodic flowering and its function is more similar to that of Arabidopsis CRY2. Moreover, SbCRY1b-overexpressed transgenic Arabidopsis showed oversensitivity to abscisic acid (ABA) during seed germination and root development. The expression of abscisic acid-insensitive 4 (ABI4), ABI5, abscisic acid responsive element-binding 1 (ABF1), (sucrose non-fermenting 1)-related protein kinase (SnRK2.3), RD29A, and EM6 was upregulated in the transgenic Arabidopsis. The results demonstrated that SbCRY1b may integrate blue light and ABA signals to regulate plant development.