Date of Award

2019

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Biological Sciences (MS)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Chandrashekhar Joshi

Advisor 2

Guiliang Tang

Committee Member 1

Rupali Datta

Abstract

Short Tandem Target Mimic (STTM) is a commonly technique used for functional studies of a number of genes in several plant model systems. However, very little is known about application of STTM technique in tree species. In this study, STTM was applied to knock down microRNA396 (miR396) in transgenic poplar trees for the first time. STTM396 expression resulted in dramatic decrease in miR396 expression levels leading to taller plants with larger leaves and larger leaf cell size. Additionally, an expression analysis of growth regulating factor genes (GRFs) that are members of miR396 target gene family showed up-regulation of GRF07 gene suggesting that miR396 might be negatively regulating growth and cell expansion in leaves via GRF07 suppression. On the contrary, down-regulation of GRF06 and GRF18 was observed in the same transgenic trees suggesting the complexity of gene regulatory relationship between expression of miR396 and GRFs in poplar. Remarkably, GRF10 and GRF17 were barely expressed in leaves tissues suggesting they might be expressed in other tissues in a tissue-specific manner. Overall, these results suggest that the STTM is an effective approach for functional analyses of miRNAs in poplars, a model tree species. In addition, miR396 may be playing some important roles in growth and cell expansion of leaves via regulating expression of GRF genes in poplars.

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