Genetics and functional genomics of abscission.

摘要

The iconic shedding of leaves by trees every fall is a form of abscission. This is a process by which plants discard organs in response to environmental effects or the normal developmental plan. Long studied at the anatomical and physiological levels, it has only been in the last two decades with the use of the model plant Arabidopsis that it is being understood at a molecular and genetic level. The history and current state of the field is reviewed in Chapter 1. To further understand this mechanism, multiple genetic and genomic approaches were utilized and are described in Chapters 2 through 5.;In Chapter 2 two different mutagenesis techniques, ems mutagenesis and activation tagging were utilized to try to discover new genes involved in abscission. In the first, plants were screened for loss of abscission phenotypes. Numerous abscission defective mutants were found and characterized, but no new genes were identified. However, new alleles of two known genes, HAESA (HAE) and HAESA-LIKE 2 ( HSL2), were found and will be useful for further experiments. Another floral developmental phenotype was mapped to a region containing the gene HAWAIIAN SKIRT (HWS) and a mutant allele of this gene was identified. In the activation tagging screen, plants were screened for suppression of the phenotype from a loss of abscission double mutant, hae hsl2..;In Chapter 3, RNA-Seq was used to study the effects of the hae hsl2 mutant on gene expression in stage 15 floral receptacles. 2034 genes were identified as differentially expressed, 349 of which having changes of 2 fold or greater. These genes were categorized as being HAE HSL2-dependent and were enriched for functions in cell wall modification and defense responses. Expression of HAE HSL2-dependent glycosyl hydrolases was further studied in earlier developmental stages and mutants of INFLORESCENCE DEFICIENT IN ABSCISSION (ida) by qPCR. Comparison to stamen abscission zone (AZ) microarrays enabled the identification of genes unaffected by hae hsl2 that were categorized as HAE HSL2-independent genes. These genes were enriched for other functions such as hormonal signaling, senescence, and callose deposition.;Chapters 4 and 5 expand upon the results of Chapter 3. In Chapter 4, qPCR was used to test the expression of genes involved in HAE HSL2 signaling and HAE HSL2- independent processes. Results in Chapter 3 were largely confirmed by qPCR. Results for the genes BP/KNAT1, KNAT2, and KNAT6 challenge proposed mechanisms of action for these genes in abscission. In Chapter 5, promoter regions and gene expression are used to identify candidate transcription factors regulating HAE HSL2-dependent gene expression. Further testing of candidate genes will be needed to understand if these genes have any role in abscission.