Expression of the rice cystatin, Oryzacystatin-I (OC-I) influences the plant growth and development

Abstract

Plants contain large numbers of proteases that fulfil a wide range of functions. Cysteine proteases and their endogenous inhibitors, phytocystatins, are involved in the control of protein turnover, but their precise functions remain poorly characterized. To study cysteine protease/phytocystatin functions in detail, the properties of Arabidopsis, wheat and soybean seeds expressing Oryzacystatin I (OC-I) were investigated. All of the transgenic seeds contained significantly more protein than the wild type, but germination was similar in all lines. The protein profiles of the seeds were broadly similar to the wild type, but the wheat and soy flour made from the transgenic seeds showed some differences in protein composition compared to that of the wild type. Moreover, a proteomic analysis of the transgenic wheat seeds revealed some differences in the accumulation of specific proteins, particularly storage proteins. The growth and development of three independent transgenic Arabidopsis lines that express the cystatin Oryzacystatin I (OC-I) in the cytosol (CYS lines) and three independent lines that express OC-I in the chloroplasts (PC lines) were characterised. The CYS and PC lines had a smaller rosette diameter with fewer leaves, and they accumulated less biomass than the wild type during vegetative growth. However, the transgenic lines had significantly more biomass than the wild type at the later (reproductive) stages of development. The CYS lines had less leaf chlorophyll and carotenoid pigments than the wild type, particularly at the later stages of development. In contrast, the PC rosettes accumulated more leaf pigments than the wild type at the later stages of leaf development. The CYS and PC rosettes flowered significantly later than the wild type. The abundance of leaf transcripts and photosynthetic proteins was changed in the CYS and PC lines. In addition, chloroplast-to-nucleus signalling, analysed by the changes in the levels of specific transcripts that encode photosynthetic proteins in the presence of chloroplast inhibitors, was extensively modified in the CYS and PC lines compared to the wild type. Moreover, photosynthetic carbon assimilation was less inhibited after exposure to high light stress in the CYS and PC lines than in the wild-type. Taken together, these data demonstrate that OC-I and its target cysteine proteases play important roles in the regulation of photosynthesis, as well as vegetative and reproductive development.