Cryptochrome photoreceptors cry1 and cry2 antagonistically regulate primary root elongation in Arabidopsis thaliana

Abstract

Cryptochromes are blue-light receptors controlling multiple aspects of plant growth and development. They are flavoproteins with significant homology to photolyases, but instead of repairing DNA they function by transducing blue light energy into a signal that can be recognized by the cellular signaling machinery. Here we report the effect of cry1 and cry2 blue light receptors on primary root growth in Arabidopsis thaliana seedlings, through analysis of both cryptochrome-mutant and cryptochrome-overexpressing lines. Cry1 mutant seedlings show reduced root elongation in blue light while overexpressing seedlings show significantly increased elongation as compared to wild type controls. By contrast, the cry2 mutation has the opposite effect on root elongation growth as does cry1, demonstrating that cry1 and cry2 act antagonistically in this response pathway. The site of cryptochrome signal perception is within the shoot, and the inhibitor of auxin transport, 1-N-naphthylphthalamic acid, abolishes the differential effect of cryptochromes on root growth, suggesting the blue-light signal is transmitted from the shoot to the root by a mechanism that involves auxin. Primary root elongation in blue light may thereby involve interaction between cryptochrome and auxin signaling pathways.

Separate functions for nuclear and cytoplasmic cryptochrome 1 during photomorphogenesis ofArabidopsisseedlings

“…3C) indicates that the promotive effect of cry1 on root growth noted by Canamero et al (29) was due to cytoplasmic cry1. At high fluence rates, blue light inhibits root elongation, which is caused by nuclear cry1 (Fig.…”

Photosynthetic sucrose acts as cotyledon-derived long-distance signal to control root growth during early seedling development in Arabidopsis

“…This interpretation explains why root growth control is uncoupled from direct photoreceptor signaling and put under the command of photosynthesis. Moreover, the emerging role of Phy/Cry-mediated photomorphogenesis as a prerequisite for photosynthetic activity may explain why the involvement of these photoreceptors shows up under particular experimental conditions (3)(4)(5)(6)(7).…”

“…S1). Light required for promoting chlorophyll synthesis and other lightdependent processes in addition to photosynthesis may then become increasingly important also for root development (5,6).…”

“…In contrast to photomorphogenesis of shoot organs, the impact of light on the development of the root has so far not been extensively investigated (1,2). Recent investigators have concluded that the effect of light on root development in seedlings is an organ-autonomous feature of photomorphogenesis controlled by the red/blue light absorbing photoreceptors phytochrome and cryptochrome (3)(4)(5)(6)(7) and mediated by hormones such as auxin and/ or gibberellin (7)(8)(9).…”

“…1 and 2 demonstrate that light produces a reversible growth-promoting signal in the cotyledons, raising questions about the nature of this signal and its transport from the cotyledons to the root tip, where growth occurs. Using photomorphogenic mutants, we first tested the previously suggested possibility (3,(5)(6)(7) that the established photomorphogenic pigments phytochrome (Phy) and cryptochrome (Cry) serve as photoreceptors for root growth responses. Compared with the wild type (WT, Columbia-0), the quadruple mutant phyA,B/cry1,2 lacks the most prominently acting photomorphogenic photoreceptors and thus shows skotomorphogenesis of the shoot also in the light (10).…”