Over-expression of Chinese cabbage phytocystatin 1 retards seed germination in Arabidopsis

Phytocystatins are plant cysteine peptidase inhibitors that are implicated in the endogenous regulation of protein turnover, programmed cell death, and in defense mechanisms against insects and pathogens. cDNA encoding the phytocystatin BrCYS1 (Brassica rapa phytocystatin 1) has been isolated from the flower buds of Chinese cabbage (B. rapa L. ssp. pekinensis). In germinating seeds, treatment with the seed germination regulatory phytohormones GA₄₊₇ and ABA resulted in a rapid decrease and a slight reduction in BrCYS1 expression, respectively. In Arabidopsis, constitutive over-expression of BrCYS1 retarded germination and seedling growth, whereas these were enhanced by suppression of BrCYS1. In addition, over-expression of BrCYS1 caused a general retardation of overall plant growth and development; the opposite effect was observed in transgenic plants in which BrCYS1 expression was suppressed. Additionally, stored cysteine peptidase activity was inhibited by BrCYS1 in transgenic Arabidopsis. Based on these data, we suggest that BrCYS1 participates in the control of seed germination by regulating stored cysteine peptidase activity.