Retracted: Proline responding1Plays a Critical Role in Regulating General Protein Synthesis and the Cell Cycle in Maize    

Abstract

Proline, an important amino acid, accumulates in many plant species. Besides its role in plant cell responses to environmental stresses, the potential biological functions of proline in growth and development are unclear. Here, we report cloning and functional characterization of the maize (Zea mays) classic mutant proline responding1 (pro1) gene. This gene encodes a D 1-pyrroline-5-carboxylate synthetase that catalyzes the biosynthesis of proline from glutamic acid. Loss of function of Pro1 significantly inhibits proline biosynthesis and decreases its accumulation in the pro1 mutant. Proline deficiency results in an increased level of uncharged tRNA pro AGG accumulation and triggers the phosphorylation of eukaryotic initiation factor 2a (eIF2a) in the pro1 mutant, leading to a general reduction in protein synthesis in this mutant. Proline deficiency also downregulates major cyclin genes at the transcriptional level, causing cell cycle arrest and suppression of cell proliferation. These processes are reversible when external proline is supplied to the mutant, suggesting that proline plays a regulatory role in the cell cycle transition. Together, the results demonstrate that proline plays an important role in the regulation of general protein synthesis and the cell cycle transition in plants. INTRODUCTION In maize (Zea mays), a series of seed mutants with a starchy endosperm have been identified, and the cause of the opa-que/floury kernel phenotype has been investigated through analyzing the functions of cloned genes. Previous studies suggested that most of the opaque and floury mutants (opa-que2, floury2, Mucronate, and Defective endosperm B30) involve genes that regulate zein synthesis, such as regulatory genes or structural genes for these storage proteins (Schmidt et al., 1987; Coleman et al., 1995; Gillikin et al., 1997; Kim et al., 2004, 2006). Downregulation of zein gene (a-, b-, d-, and g-zein genes) expression by RNA interference also reproduced an opaque phenotype (Segal et al., 2003; Wu and Messing, 2010). These results indicate that the opaque/floury phenotypes of opaque2 (o2), floury2 (fl2), Defective endo-sperm B30, and Mucronate mutants are caused by either quantitative or qualitative alterations in zein proteins. However , other opaque/floury mutants, such as o1, o5, and fl1, show no notable alterations in zein proteins (Holding et al.

Proline and chitosan enhanced efficiency of microspore embryogenesis induction and plantlet regeneration in Brassica napus L.

“…More recently, flow cytometric analysis of endoreduplication and mitotic cycle in classic mutant proline responding 1 (pro1, which catalyses the biosynthesis of proline from glutamic acid) of Zea mays indicated that the G1/S transition is arrested and thus cell proliferation suppressed in pro1 mutant plantlets. Gene expression profile analyses also showed that transcripts of cell cycle related genes, including cyclins, nucleosome assembly genes, and DNA replication-related genes, were significantly down-regulated in the pro1 plantlets (Wang et al 2014) indicating the important role(s) of proline during the normal plant growth. According to our results, proline was not effective on normal plantlet regeneration at high levels so that, the majority of MDEs (78 %) underwent callusing in the cultures exposed to 500 mg l -1 proline for 5 days.…”

Mechanism of Cytoplasmic mRNA Translation

“…Despite early reports of a "PKR-like" activity in virus-infected plants (Hiddinga et al, 1988;Langland et al, 1995;Langland et al, 1996;Chang et al, 1999), no specific kinase could be purified and the sequence of a putative PKR ortholog is absent from plant genomes (Immanuel et al, 2012). GCN2 is therefore the only recognizable plant eIF2α kinase at this time and targets a similar serine residue in plant eIF2α (Halford et al, 2004;Byrne et al, 2012;Li et al, 2013a;Wang et al, 2014). Other eIF2α kinases may exist,…”

OPAQUE11 Is a Central Hub of the Regulatory Network for Maize Endosperm Development and Nutrient Metabolism

“…ZmICE1) ( Figure 12B and opaque endosperm (Schmidt et al, 1987;Miclaus et al, 2011;Myers et al, 522 2011; Wang et al, 2011;Wang et al, 2012;Wang et al, 2014;Yao et al, 2016 O11 is ectopically expressed in maize leaves (Grimault et al, 2015 under normal conditions during endosperm development (Qu et al, 2016).…”

“…Immunoblot analyses were performed as 737 described previously (Wang et al, 2014) using antibodies against the following nuclear proteins of 15 DAP maize immature kernels was carried out using a 754 previously described method (Qi et al, 2016b). …”