Molecular physiology of banana fruit ripening : improvement of fruit quality

It is now assumed that the quality of fruit is a complex trait in which a lot of mechanisms are involved, some of them being antagonistic. All of these mechanisms are the results the coercive action of differentially regulated genes. Understanding at molecular level of the mechanisms that control the target quality trait is an essential work beforehand to any plan of improvement of fruit quality trait using plant genetic strategies such as candidate-gene approach and or marker assisted selection. Presently we investigate at molecular level the ethylene responsiveness, and sugar and phenylpropanoïd metabolisms, three ripening aspects involved in functional, nutritional and organoleptic qualities of banana fruit. As a first part of this project, we report here the cloning and sequencing of genes that are differentially expressed during fruit ripening, as tools for functional genomic studies and putative molecular marker developments. Different molecular biology approaches haves been used to isolate ripening these ripening related-genes. They include cDNA amplification (RT- and RACE-PCR) and, construction of complete and subtractive suppressive cDNA libraries (SSH). Sequencing and BLAST analysis of some of these isolated cDNA clones revealed that 205 of them presented a high homology with different genes in database. Many of the predicted proteins encoded by these genes are putatively involved in the regulation of gene expression, hormonal metabolism, hormonal-signal transduction, sugar metabolism and other ripening process. Among these 205 genes, 11 are still unclassified since presenting homology to unknown proteins of rice or Arabidopsis. Finally, thirteen additional clones were putatively novel, since they failed to match with database sequences. Expressions of a few of the matching clones have been followed in relation with ethylene responsiveness of fruit. Our results show that the expression of these genes is under ethylene and development (or both) control. These cDNA clones provide us with a basis for future work that will combine physiological, genomic and genetic approaches to identify key candidate-genes involved in the expression of banana quality trait. (Résumé d'auteur

A framework for forensic face recognition based on recognition performance calibrated for the quality of image pairs

Recently, it has been shown that performance of a face recognition system depends on the quality of both face images participating in the recognition process: the reference and the test image. In the context of forensic face recognition, this observation has two implications: a) the quality of the trace (extracted from CCTV footage) constrains the performance achievable using a particular face recognition system; b) the quality of the suspect reference set (to which the trace is matched against) can be judiciously chosen to approach optimal recognition performance under such a constraint. Motivated by these recent findings, we propose a framework for forensic face recognition that is based on calibrating the recognition performance for the quality of pairs of images. The application of this framework to several mock-up forensic cases, created entirely from the MultiPIE dataset, shows that optimal recognition performance, under such a constraint, can be achieved by matching the quality (pose, illumination, and, imaging device) of the reference set to that of the trace. This improvement in recognition performance helps reduce the rate of misleading interpretation of the evidence

Expression patterns of ethylene biosynthesis genes from banana during fruit ripening and in relationship with finger drop

Banana finger drop is expressed as a dislodgement of individual fruits from the hand at the pedicel rupture area. As bananas fruit are marketed in hands of generally 4?9 fruits, this postharvest disorder considerably reduces the commercial value of the product. Together with a burst of ethylene production, finger drop phenomenon was found to be one of the main features closely associated with banana ripening. We have shown that finger drop process occur early after ripening induction and imply ethylene?regulated gene. In this study, we investigate at molecular level the putative relationship between ethylene and finger drop processes during ripening of Cavendish banana fruit. To this end, expression of ethylene biosynthesis genes (MaACO1, MaACO2, MaACS1, MaACS2, MaACS3 and MaACS4) was examined at median area (control zone) and compared to that in the pedicel rupture area (drop zone). During the 4 first days following the ripening induction, transcripts of all genes were detected in both zones, but accumulated differentially. MaACO2 mRNA levels did not change in either zone. Levels of MaACO1, MaACS1, MaACS2, MaACS4 mRNAs accumulated highly in the drop zone. A high the mRNA of MaACS3 gene accumulated highly in drop zone only at the harvest time. One day after ripening induction, this level decreased drastically at comparable level to that observed at median zone, and remain constant in both zones throughout postharvest ripening. The results demonstrate that finger drop process involved ripening ethylene biosynthesis. They also suggest that ethylene can be one of the regulator cues of finger drop process. (Résumé d'auteur

A note on the KP hierarchy

Given the two boson representation of the conformal algebra \hat W_\infty, the second Hamiltonian structure of the KP hierarchy, I construct a bi-Hamiltonian hierarchy for the two associated currents. The KP hierarchy appears as a composite of this new and simpler system. The bi-Hamiltonian structure of the new hierarchy gives naturally all the Hamiltonian structures of the KP system.Comment: 12 pages, no figure

The Spectral Evolution along the Z track of the Bright Neutron Star X-ray Binary GX 17+2

Z sources are bright neutron-star X-ray binaries, accreting at around the Eddington limit. We analyze the 68 RXTE observations (270 ks) of Sco-like Z source GX 17+2 made between 1999 October 3-12, covering a complete Z track. We create and fit color-resolved spectra with a model consisting of a thermal multicolor disk, a single-temperature-blackbody boundary layer and a weak Comptonized component. We find that, similar to what was observed for XTE J1701-462 in its Sco-like Z phase, the branches of GX 17+2 can be explained by three processes operating at a constant accretion rate Mdot into the disk: increase of Comptonization up the horizontal branch, transition from a standard thin disk to a slim disk up the normal branch, and temporary fast decrease of the inner disk radius up the flaring branch. We also model the Comptonization in an empirically self-consistent way, with its seed photons tied to the thermal disk component and corrected for to recover the pre-Comptonized thermal disk emission. This allows us to show a constant Mdot along the entire Z track based on the thermal disk component. We also measure the upper kHz QPO frequency and find it to depend on the apparent inner disk radius R_in (prior to Compton scattering) approximately as frequency \propto R_in^(-3/2), supporting the idenfitication of it as the Keplerian frequency at R_in. The horizontal branch oscillation is probably related to the dynamics in the inner disk as well, as both its frequency and R_in vary significantly on the horizontal branch but become relatively constant on the normal branch.Comment: 17 pages, 14 figures. Accepted for publication in Ap