HUA, Miaoyuan
(2021)
GENE NETWORKS CONTROLLING ANTHER TAPETUM DEVELOPMENT IN BARLEY (Hordeum vulgare) DURING EARLY ANTHER DEVELOPMENT.
PhD thesis, University of Nottingham.
Abstract
The tapetum, the innermost somatic cell layer in anther locule, directly communicates with the developing gametophytic cells, providing essential nutrients, critical components for their development and maturity. The cell fate of the Arabidopsis tapetum is determined by a EMS1-SERK-TPD1 receptor-like kinase (RLK) signaling cassette, with similar control described in rice. After the cell fate has been determined, the tapetum starts its further development and subsequent programmed degeneration process to provide pollen coat essential materials for the developing pollen grains. Studies have shown a relatively conserved regulatory genetic pathway, DYT1-TDF1-AMS-MS188-MS1, controlling these complex events in Arabidopsis and rice.
However, few anther development studies have been reported in barley (Hordeum vulgare). Here, we focus on the tapetum regulatory pathway and to translate the knowledge from model plants to barley via a reverse genetic approach. We first demonstrate the conserved role of HvTDF1, an R2R3 MYB family gene, which as the orthologous gene of Arabidopsis and rice TDF1 genes. We describe the expression profile of HvTDF1 and its potential role in barley anther development through mutagenesis and activation assays. The results suggest that TDF1 genes are highly conserved between monocot and dicot plants, and they play a crucial role in regulating downstream gene expression. This finding further helps us to understand the regulation role of the HvTDF1 protein in anther development.
The other gene in this study, DTT1 (DEFECTIVE TAPETUM TRANSITION1), was also characterized by a reverse genetic approach. DTT1 is a basic Helix-Loop-Helix (bHLH) family transcription factor identified as the homologous gene of tapetum specific bHLH genes. The
DTT1 protein shares high identity with three functional redundant genes, bHLH010, bHLH 089 and bHLH 091 in Arabidopsis, and two functionally distinct TIP2 and EAT1 in rice. For further understanding the function of DTT1 in barley, CRISPR-Cas9 KO lines were generated, and expression and detailed phenotypic analysis conducted. This has shown both conserved and unique aspects of the role of DTT1 in tapetum development.
In summary, both DTT1 and HvTDF1 are crucial for barley anther development at different stages. DTT1 is required for early development during anther somatic cell type transition. HvTDF1 may act as a downstream gene of DTT1, the conserved role of TDF1 suggests that the tapetum development process remains similar between monocot and dicot plants even after long a evolutionary time, nevertheless distinct aspects of these pathways are also shown between the monocot and dicot species. The barley DTT1 and HvTDF1, are two newly characterized genes that are critical for anther and pollen formation and provide valuable genetic resources for understanding grass species development from early to late anther developmental. Moreover, these two mutants could serve as an excellent genetic resource to understand tapetum development and communications between the developing MMCs and their surrounded somatic cell layer.
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