Disruption of chloroplast biogenesis and plant development upon down‐regulation of a chloroplast processing enzyme involved in the import pathway

Abstract

SummaryTypically, nuclear-encoded chloroplast proteins are synthesized as precursors and require proteolytic processing upon import before their assembly into functional complexes within the organelle. A cDNA encoding a chloroplast processing enzyme (CPE), which was originally identified as a protease that cleaves the precursor for the major light-harvesting chlorophyll binding protein (preLHCP), was introduced into the tobacco genome in an antisense orientation to investigate the role of the enzyme in vivo. The presence of the antisense-CPE gene resulted in chlorotic leaves, and retarded shoot and root growth. The introduction of the antisense-CPE gene disrupted the normal pattern of plastid division. Chloroplast numbers in cotyledon and first leaf cells were reduced 25% compared to the control plants. Chloroplasts contained fewer thylakoids and large starch grains, the latter an indication of a change in carbon flux. CPE levels and activity were significantly lower in stromal extracts in the transgenic plants. Interestingly, in vitro import of precursor proteins was defective. Most of the preLHCP remained on the exterior of the organelle, and only a small fraction of preRBCA was imported, suggesting that a change in CPE levels can influence translocation across the envelope. Our in vivo results support the conclusion that CPE plays a critical role during chloroplast biogenesis, and that the pleiotropic effects of CPE down-regulation reflect its function as a general stromal processing peptidase as part of the import machinery. Furthermore, these findings indicate the importance of regulating the expression of components of the import machinery for normal plant development.

Multiple Classes of Immune-Related Proteases Associated with the Cell Death Response in Pepper Plants

“…1). This altered phenotype showed similar developmental phenotypes to those in previous studies of down-regulation of the gene product [34], [35]. The smallest class was made up of 3 proteases (Fig.…”

In Vivo Analysis of the Role of atTic20 in Protein Import into Chloroplasts

“…This phenotype is similar to the extremely pale phenotype exhibited by the atTic20 antisense plants that fail to develop beyond the cotyledon stage ( Figure 3A, Y4). Antisense tobacco plants with reduced levels of the stromal processing protease also exhibit dramatic growth defects, a chlorotic phenotype, and reduced thylakoids (Wan et al, 1998).…”

Function of the stromal processing peptidase in the chloroplast import pathway

“…The downregulation of SPP in transgenic plants using an antisense cDNA construct has provided additional insight into the role of SPP in vivo (Wan et al 1998, Zhong et al 2003). When SPP levels were reduced fivefold in tobacco, plants were chlorotic and shoot and root growth was retarded.…”