Various tomato cultivars display contrasting morphological and molecular responses to a chronic heat stress.

Climate change is one of the biggest threats that human society currently needs to face. Heat waves associated with global warming negatively affect plant growth and development and will increase in intensity and frequency in the coming years. Tomato is one of the most produced and consumed fruit in the world but remarkable yield losses occur every year due to the sensitivity of many cultivars to heat stress (HS). New insights into how tomato plants are responding to HS will contribute to the development of cultivars with high yields under harsh temperature conditions. In this study, the analysis of microsporogenesis and pollen germination rate of eleven tomato cultivars after exposure to a chronic HS revealed differences between genotypes. Pollen development was either delayed and/or desynchronized by HS depending on the cultivar considered. In addition, except for two, pollen germination was abolished by HS in all cultivars. The transcriptome of floral buds at two developmental stages (tetrad and pollen floral buds) of five cultivars revealed common and specific molecular responses implemented by tomato cultivars to cope with chronic HS. These data provide valuable insights into the diversity of the genetic response of floral buds from different cultivars to HS and may contribute to the development of future climate resilient tomato varieties.

A possible role for L24 of Bacillus subtilis in nucleoid organization and segregation.

The condensation of DNA in bacterial nucleoids during cell cycle is a complex and dynamic process. Proteins displaying the physico-chemical properties of histones are known to contribute to this process. During a search for B. subtilis nucleoid associated proteins, HBsu and L24 were identified as the most abundant proteins in nucleoid containing fractions. Purified L24 binds and condenses DNA in vitro. In this paper we describe immunofluorescence studies that demonstrated that L24 is located at the poles of the nucleoids in exponentially growing cells. In contrast, the protein is dispersed in the cytoplasm during stationary phase. Moreover, overexpression of the rplX gene encoding L24 disrupts nucleoid segregation and positioning.

Characterization of LrpC DNA-binding properties and regulation of Bacillus subtilis lrpC gene expression.

The lrpC gene was identified during the Bacillus subtilis genome sequencing project. Previous experiments suggested that LrpC has a role in sporulation and in the regulation of amino acid metabolism and that it shares features with Escherichia coli Lrp, a transcription regulator (C. Beloin, S. Ayora, R. Exley, L. Hirschbein, N. Ogasawara, Y. Kasahara, J. C. Alonso, and F. Le Hégarat, Mol. Gen. Genet. 256:63-71, 1997). To characterize the interactions of LrpC with DNA, the protein was overproduced and purified. We show that LrpC binds to multiple sites in the upstream region of its own gene with a stronger affinity for a region encompassing P1, one of the putative promoters identified (P1 and P2). By analyzing lrpC-lacZ transcriptional fusions, we demonstrated that P1 is the major in vivo promoter and that, unlike many members of the lrp/asnC family, lrpC is not negatively autoregulated but rather slightly positively autoregulated. Production of LrpC in vivo is low in both rich and minimal media (50 to 300 LrpC molecules per cell). In rich medium, the cellular LrpC content is six- to sevenfold lower during the exponentional phase than during the stationary growth phase. Possible determinants and the biological significance of the regulation of lrpC expression are discussed.

The L17 ribosomal protein of Bacillus subtilis binds preferentially to curved DNA.

We searched in Bacillus subtilis for proteins that bind preferentially to curved DNA. Two proteins of 9 and 15 kDa displaying this property were purified from exponentially growing cells of B. subtilis strain 168. Sequencing of N-terminal amino acids identified them as the proteins HBsu and L17 respectively. The overproduction of L17 from B. subtilis in Escherichia coli was shown to have a strong effect on nucleoid morphology and segregation.

Overproduction, purification and characterization of the HPB12-L24 ribosomal protein of Bacillus subtilis.

HPB12-L24 was previously described as a bifunctional histone-like and ribosomal protein in Bacillus subtilis. In order to confirm the identity of HPB12 and L24, and to study the properties of this protein, the rplX gene of B. subtilis encoding L24 has been overexpressed in Escherichia coli by an efficient protein overproduction system. A simple and rapid purification scheme using ammonium sulfate precipitation and cation-exchange chromatography is presented. 10 mg of pure L24 per g of Escherichia coli cells were obtained. The purified recombinant protein L24 is heat-stable, acid-soluble and binds preferentially supercoiled DNA like protein HPB12. These results confirm the identity of HPB12 and L24. Overexpression of rplX led to gross alterations of cell morphology and to an abnormal shape of nucleoids.