Opposing roles of phytochrome A and phytochrome B in early cryptochrome-mediated growth inhibition

Km. Folta et Ep. Spalding, Opposing roles of phytochrome A and phytochrome B in early cryptochrome-mediated growth inhibition, PLANT J, 28(3), 2001, pp. 333-340
Citations number
Categorie Soggetti
Plant Sciences","Animal & Plant Sciences
Journal title
ISSN journal
0960-7412 → ACNP
Year of publication
333 - 340
SICI code
The cryptochrome 1 (cry1) photoreceptor is responsible for the majority of the inhibitory effect of blue light on hypocotyl elongation, but phytochrom e photoreceptors also contribute to the response through a phenomenon known as coaction. In Arabidopsis thaliana the participation of phytochromes A a nd B (phyA and phyB) in the early phase of cry1 action was investigated by determining the effects of phyA, phyB and hy1 mutations on a cry1-dependent membrane depolarization, which is caused by the activation of plasma-membr ane anion channels within seconds of blue light treatment. High-resolution growth measurements were also performed to determine the timing of the requ irement for phytochrome in cry1-mediated growth inhibition, which is causal ly linked to the preceding anion-channel activation. A null mutation in PHY A impaired the membrane depolarization and prevented the early cry1-depende nt phase of growth inhibition as effectively and with the same time course as mutations in CRY1. Thus, phyA is necessary for cry1/cry2 to activate ani on channels within the first few seconds of blue light and to suppress hypo cotyl elongation for at least 120 min. This finding furthers the notion of an intimate mechanistic association between the cry and phy receptors in me diating light responses. The absence of phyB did not affect the depolarizat ion or growth inhibition during this time frame. Instead, double mutant ana lyses showed that the phyB mutation. suppressed the early growth phenotypes of both phyA and cry1 seedlings. This result is consistent with the emergi ng view that the prevailing growth rate of a stem is a compromise between l ight-dependent inhibitory and promotive influences. It appears that phyB op poses the cry1/phyA-mediated inhibition by promoting growth during at least the first 120 min of blue light treatment.