Date of Award

December 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dazhong Zhao

Abstract

Strawberry is an important fruit crop in the Rosaceae family. Originally from the temperate region, strawberry is vulnerable to heat waves, which reduce fruit yield and quality. Previous studies have shown that heat stress impairs pollen development; however, the molecular mechanisms by which heat stress affects the development of anthers, where pollen develops, are unclear. Due to the genome complexity of cultivated strawberry (Fragaria × ananassa, 2n = 8x= 56), Fragaria vesca (2n = 2x = 14) was used, which emerges as a diploid model plant for Rosaceae, to study the effects of heat stress on anther development at morphological and molecular levels. In this study, a complete anther development series was established, which helped identify key stages affected by heat stress via defining morphological hallmarks at each developmental stage. It was demonstrated that heat stress led to male sterility in Fragaria vesca by affecting anther development at two key stages- meiotic stage-6 and post-meiotic stage-8. Morphological changes of anther cell differentiation caused by heat stress at these two key stages were further revealed using backscattered scanning electron microscopy imaging. Finally, a stage-specific transcriptomics approach was utilized to study the underlying molecular mechanisms of responses to heat stress. Heat stress altered expression of many genes, including those encoding heat shock proteins, transcription factors, genes involved in cell wall, and histone modification enzymes. My thesis work lays the groundwork for future discoveries in heat stress associated with male sterility within the Rosaceae family. The genes identified as key players in response to heat stress can be targeted in efforts to improve heat tolerance in crops.

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