PHYTOCHROME KINASE SUBSTRATE4 Modulates Phytochrome-Mediated Control of Hypocotyl Growth Orientation1[W][OA]

Gravity and light are major factors shaping plant growth. Light perceived by phytochromes leads to seedling deetiolation, which includes the deviation from vertical hypocotyl growth and promotes hypocotyl phototropism. These light responses enhance survival of young seedlings during their emergence from the soil. The PHYTOCHROME KINASE SUBSTRATE (PKS) family is composed of four members in Arabidopsis (Arabidopsis thaliana): PKS1 to PKS4. Here we show that PKS4 is a negative regulator of both phytochrome A- and B-mediated inhibition of hypocotyl growth and promotion of cotyledon unfolding. Most prominently, pks4 mutants show abnormal phytochrome-modulated hypocotyl growth orientation. In dark-grown seedlings hypocotyls change from the original orientation defined by seed position to the upright orientation defined by gravity and light reduces the magnitude of this shift. In older seedlings with the hypocotyls already oriented by gravity, light promotes the deviation from vertical orientation. Based on the characterization of pks4 mutants we propose that PKS4 inhibits changes in growth orientation under red or far-red light. Our data suggest that in these light conditions PKS4 acts as an inhibitor of asymmetric growth. This hypothesis is supported by the phenotype of PKS4 overexpressers. Together with previous findings, these results indicate that the PKS family plays important functions during light-regulated tropic growth responses

Production of Crown-Rot Resistant Strawberry by Concentration of Indigenously Existing Resistant Cells through Tissue Culture

[Synopsis] Tissue culture was used for selecting and enhancing the resistant variant cells which indigenously exist in leaf tissues of the susceptible cultivar in order to establish an efficient system for producing crown-rot resistant lines of strawberry. Leaves of the resistant and susceptible cultivars were inoculated with the crown-rot pathogen by needle-prick inoculation method. Two types of lesions (small necrotic spots and extensively expanding lesions) were formed on leaves of both the resistant and susceptible cultivar. The resistant cultivar was characterized by higher percentage of the small necrotic spots. The cells forming the resistant-type lesion were amplified by inducing callus tissues from leaf explants of the susceptible cultivar, and regenerants showing the higher frequencies of the resistant-type lesion were selected. The amplification of these cells to the level of the resistant cultivar was achieved by repeating callus induction and plant regeneration from the selected repenerants. The regenerants finally obtained in the present system showed the resistance in the field inoculation test