Chiara Lanzanova

A maize histone deacetylase and retinoblastoma-related protein physically interact and cooperate in repressing gene transcription

In mammalian cells the product of the human retinoblastoma tumour suppressor gene (pRb) can recruit Rpd3-like histone deacetylases to repress transcription. In this study, we investigated whether this mechanism might also be relevant in plants and found both conserved and distinct features. The expression profiles of the Zea mays Rpd3-type histone deacetylase (ZmRpd3I) and the retinoblastoma-related (ZmRBR1) homologues were analysed during endosperm development. GST pull-down and immunoprecipitation experiments showed a physical interaction between ZmRBR1 and ZmRpd3I. Because ZmRpd3I lacks a LXCXE motif, conserved in several pRb-interacting proteins, we have mapped the amino acid domains involved in the ZmRBR1/ZmRpd3I interaction. Furthermore, we observed that ZmRbAp1, a maize member of the MSI/RbAp family, facilitated this protein interaction. Co-transformations of tobacco protoplasts with plasmids expressing ZmRBR1 and ZmRpd3I showed that the two proteins cooperate in repressing gene transcription. Our findings represent the first indication that in plants a regulator of important biological processes, ZmRBR1, can recruit a histone deacetylase, ZmRpd3I, to control gene transcription.

Regulation and Processing of Maize Histone Deacetylase Hda1 by Limited Proteolysis

A maize histone deacetylase gene was identified as a homolog of yeast Hda1. The predicted protein corresponds to a previously purified maize deacetylase that is active as a protein monomer with a molecular weight of 48,000 and is expressed in all tissues of germinating embryos. Hda1 is synthesized as an enzymatically inactive protein with an apparent molecular weight of 84,000 that is processed to the active 48-kD form by proteolytic removal of the C-terminal part, presumably via a 65-kD intermediate. The enzymatically inactive 84-kD protein also is part of a 300-kD protein complex of unknown function. The proteolytic cleavage of ZmHda1 is regulated during maize embryo germination in vivo. Expression of the recombinant full-length protein and the 48-kD form confirmed that only the smaller enzyme form is active as a histone deacetylase. In line with this finding, we show that the 48-kD protein is able to repress transcription efficiently in a reporter gene assay, whereas the full-length protein, including the C-terminal part, lacks full repression activity. This report on the processing of Hda1-p84 to enzymatically active Hda1-p48 demonstrates that proteolytic cleavage is a mechanism to regulate the function of Rpd3/Hda1-type histone deacetylases.

Levels of total fumonisins in maize samples from Italy during 2006-2008.

We analysed a total of 2258 grain samples over a 3-year period (2006–2008) from 93 storage centers in the principal maize cultivation area of Italy to establish the levels of fumonisin contamination. Fumonisin concentrations were measured using ELISA (RIDASCREEN) fumonisin test kits. Mean levels of contamination were remarkably high in each year, with the highest value in 2006 (10.9 mg/kg) and the lowest in 2008 (4.8 mg/kg). Similarly, for each year, variations were quite large: from <LOQ to 77.0 mg/kg, < LOQ to 26.3, and 0.1 to 19.0 mg/kg, respectively, in 2006, 2007 and 2008. The highest fumonisin concentration was found in samples harvested in Veneto (11.1 mg/kg) and Friuli Venezia Giulia (8.9 mg/kg), while the lowest were recorded in Emilia Romagna and Piemonte (4.6 mg/kg).

Ribosome-Inactivating Proteins in Cereals

Plants constitutively accumulate proteins that are either toxic or inhibitory against pathogens, including ribosome-inactivating proteins (RIPs) and N-glycosidases that depurinate the universally conserved α-sarcin loop of large rRNAs. Cereal RIPs share a high similarity with all the other RIPs; however, they retain characteristic features forming a distinct class which diversified significantly during evolution. They appear involved in several different physiological roles, such as defense against pathogens and/or involved in regulatory and developmental processes. RIPs from cereals generally have low activity against plant ribosomes. In this chapter are reported recent advances in research related to cereal RIPs, with particular emphasis to the maize RIP (b-32) expressed in transgenic plants as an antifungal protein and reliable tool in crop disease management programs.

Quality Evaluation and High Throughput Analysis of Aromatic Italian Rice Varieties Through HS-SPME/GC-MS Analysis

ABSTRACT Headspace solid phase micro-extraction (HS-SPME) coupled with gas chromatography/mass spectrometry (GC-MS) was assessed as a technique to analyze the volatile aroma profile of Italian aromatic rice varieties. The HS-SPME/GC-MS technique gives data comparable to data obtained with conventional extraction methods but produces samples with higher compound concentration, lower levels of contamination, and shorter sample preparation time. The technique might prove useful in helping to assess the commercial potential of aromatic rice varieties on the international market.