Identification of genes associated with cotyledon senescence in upland cotton

Abstract

In order to unravel the biochemical pathways and understand the molecular mechanisms involved in leaf senescence, suppression subtractive hybridization (SSH) was used to generate a cDNA library enriched for transcripts differentially expressed in developmental senescence cotyledons of upland cotton. After differential screening by membrane-based hybridization and subsequent confirmation by reverse Northern blot analysis, selected 678 clones were sequenced and analyzed. Sequencing of these cDNA fragments reveals that 216 of expressed sequence tags (ESTs) represented unique genes. Of these 216 cDNAs, 151 clones (69.9%) show significant homologies to previously known genes, while the remaining 65 do not match any known sequences. 151 unique ESTs are assigned to twelve different categories based on their putative functions generated by BLAST analysis. These SAG-encoded proteins are likely to participate in macromolecule degradation, nutrient recycling, detoxification of oxidative metabolites, and signaling and regulatory events. The expression pattern of selection of genes was confirmed using northern hybridization. Northern hybridization confirmed several distinct patterns, from expression at a very early stage to the terminal phase of the senescence syndrome. Clones encoding proteases and proteins involved in macromolecule degradation and gluconeogenesis, as well as stress-related genes, are up regulated in senescence cotyledons.