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Quantitative Trait Loci (QTLs) for pollen thermotolerance detected in maize
No full textPollen thermotolerance is an important component of the adaptability of crops to high temperature stress. The tolerance level of the different genotypes in a population of 45 maize recombinant inbred lines was determined as the degree of injury caused by high temperature to pollen germinability (IPGG) and pollen tube growth (IPTG) in an in vitro assay. Both traits revealed quantitative variability and high heritability. The traits were genetically dissected by the analysis of molecular markers using 184 mapped restriction fragment length polymorphisms (RFLPs). Significant genetic correlation between the markers and the trait allowed us to identify a minimum number of five quantitative trait loci (QTLs) for IPGG and six QTLs for IPTG. Their chromosomal localization indicated that the two characters are controlled by different sets of genes. In addition, IPGG and IPTG were shown to be basically independent of the pollen germination ability and pollen tube growth rate under non-stress conditions. These results are discussed in relation to their possible utilization in a breeding strategy for the improvement of thermotolerance in maize
Quantitative expression of maize HSPs : genetic dissection and association with thermotolerance
No full textIn higher plants, within-species qualitative polymorphism for heat shock proteins (HSPs) is extremely rare, even between genotypes showing different heritable levels of thermotolerance. Here we have explored the amount of quantitative variability in HSP synthesis in maize. We have analyzed the quantitative expression of the typical HSPs in a set of recombinant inbreds (RIs) derived from the f1 hybrid between a thermotolerant (T232)- and a thermosensitive (CM37)-genotype, characterized for about 200 mapped RFLP loci. Significant differences were detected in the level of expression of five HSPs, and their frequency distribution in the RI population is that of a quantitative trait. Subsequent mapping of loci controlling the characters, based on RFLP analysis, confirmed the multigenic control of HSP expression: the regression analysis of the band intensities of each variant HSP on RFLPs revealed, for the different HSPs, a minimum number of three to eight quantitative trait loci (QTLs) accounting for a high proportion (0.35-0.60) of the genetic variability of these bands. An analysis of the correlation between the variability of HSPs and that of cellular membrane stability, a cellular component of thermotolerance, did not reveal any significant association of the two parameters
Introduzione
No full textSi presentano i 10 contributi raccolti nel volume in oggetto delineandone il percorso metodologico e continutistico ed inserendolo nel panorama storiografico di riferimento
Molecular analysis and mapping of gst genes
No full textThe glutathione(GSH)-glutathione-S-transferase(GST) system is a detoxification system capable of inactivating many toxic molecules. It is present in a wide variety of organisms, from mammals to insects and plants, in which it is involved in conferring tolerance to different classes of herbicides, including s-triazines, acetanilides and thiocarbamates. In maize, three gst genes (gst1, gstII, gstIII) (Shah et al., Plant Mol Biol 6:203-211, 1986; Moore et al. Nucleic Acids Res. 14:7277-7235,1986; A. Greenland, personal communication) have been identified and sequenced. [Ed. note: Temporary symbols pending clarifications of gene relationships.] They belong to a gene family and show extensive sequence homology at both DNA and protein levels. They encode for four isozymes which are active as dimers: GSTI, GSTIII and GSTIV are homodimers of 29, 26 and 27 kDa subunits respectively, while GSTII is a heterodimer of 29 (same as GSTI) and 27 (same as GSTIV) kDa subunits.
We found evidence that the number of maize gst genes and isozymes is higher, some isoforms being tissue-specific while others are expressed in most tissues. In particular, the two major bands detectable in electrophoretic enzyme assay (native PAGE) are expressed in roots, leaves and scutella. By screening numerous maize genotypes we have identified two inbred lines, B37 and B83, lacking these two bands in all tissues. Analysis of null/+ and null/null F1s indicated that the null mutations are recessive and allelic in the two inbreds. In order to identify to which of the characterized GST isoforms these bands correspond, we have carried out Northern experiments to analyze the transcription pattern of gstI and gstII in roots of normal and of the two null lines. As specific probes we have used a cDNA clone of gstII (kindly provided by A. Greenland) and a probe including the first exon of gstI synthesized via PCR on the basis of the published sequence information. gstII transcript was detected in all genotypes, while gstI mRNA was absent in the null lines. These data indicate that a single gene, gstI, controls the expression of the two isoforms. We tentatively identify them as GSTI (29 kDa homodimer) and GSTII (29/27 heterodimer).
The genomic organization of the two genes was investigated by Southern analysis: gst1 is a single copy gene, while the hybridization pattern of gstII suggests the presence of a duplicated gene. We have mapped these genes by RFLP analysis using an F2 population of 149 individuals, previously characterized for 110 molecular markers. gst1 was placed on the long arm of chromosome 8, while the two putative gstII loci, gstIIA and gstIIB, were mapped on chromosome 8 (70cM from gst1) and on chromosome 10 respectively
Molecular markers (RFLPs and HSPs) for the genetic dissection of thermotolerance in maize
No full textCellular membrane stability (CMS) is a physiological index widely used to evaluate thermostability in plants. The genetic basis of the character has been studied following two different approaches: restriction fragment length polymorphism (RFLP) analysis, and the effects of segregating heat shock protein (HSP) loci. RFLP analysis was based on a set of recombinant inbreds derived from the T32 x CM37 F1 hybrid and characterized for about 200 RFLP loci. Heritability of CMS estimated by standard quantitative analysis was 0.73. Regression analysis of CMS on RFLPs detected a minimum number of six quantitative trait loci (QTL) accounting for 53% of the genetic variability. The analysis of the matrices of correlation between RFLP loci, either within or between chromosomes, indicates that no false assignment was produced by this analysis. The effect of HSPs on the variability of the CMS was tested for a low-molecular-weight peptide (HSP-17) showing presence-absence of segregation in the B73 x Pa33 F2 population. Although the genetic variability of the character was very high (h2 = 0.58) the effect of HSP-17 was not significant, indicating either that the polypeptide is not involved in the determination of the character or that its effect is not statistically detectable
Sporophytic and gametophytic components of thermotolerance affected by pollen selection
No full textThis study was undertaken to assess the effect of in vivo male gametophytic selection on components of thermotolerance in maize, The F-1 between a tolerant (Pa33) and a susceptible (B37) genotype was used as pollen source, Male gametophytic selection was carried out by applying a two-h treatment of 50 degrees C to immature tassels in the field, The resulting F-2 and backcross generations were evaluated for sporophytic and gametophytic components of thermotolerance, including cellular membrane stability, heat shock protein synthesis, pollen germination, and tube growth rate, Both expression of heat shock proteins 102, 84, and 17 kDa and pollen germination ability under a high-temperature regime were significantly higher in the selected than in the nonselected progenies, No response to selection was detected for cellular membrane stability and pollen tube growth rate, These results suggest that pollen selection can serve to improve at least some gametophytic and sporophytic components of thermotolerance
Transcription profiling of rice metal transporters genes putatively involved in cadmium accumulation
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Dns Victoria. Legende monetali, iconografia e storia nelle coniazioni della Langobardia meridionale del IX secolo
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