Bioscience Evidence 2024, Vol.14, No.5, 218-226 http://bioscipublisher.com/index.php/be 222 5.2 Overexpression and knockdown studies Overexpression and knockdown studies are essential to understand the functional dynamics of OsHIPP16. In rice, the miRNA osa-miR171c targets four GRAS transcription factors, including OsHAMgenes, to control the floral transition and maintenance of shoot apical meristem (SAM) indeterminacy (Fan et al., 2015). Overexpression of osa-miR171c leads to prolonged vegetative phases and delayed heading dates, while knockdown results in altered expression of key developmental regulators. These findings imply that manipulating OsHIPP16 expression could similarly affect ovule development and floral transition, providing further evidence of its functional role. 5.3 Functional complementation assays Functional complementation assays can validate the specific role of OsHIPP16 in ovule development. In the case of OsMADS13, functional assays demonstrated that the gene's expression is restricted to ovules and that its mutation leads to significant phenotypic changes (Dreni et al., 2007). By conducting similar assays with OsHIPP16, researchers can determine whether the gene can rescue the ovule identity defects observed in mutants, thereby confirming its functional importance in ovule development. 6 Comparative Analysis with Other HAM Domain Genes 6.1 Similarities and differences in HAM domain gene functions The HAM domain gene OsHIPP16 in rice plays a crucial role in ovule development, similar to other HAM domain genes identified in various plant species. For instance, the D-lineage MADS-box gene OsMADS13 in rice, which is orthologous to the Arabidopsis gene STK and Petunia genes FBP7 and FBP11, is essential for ovule identity. Mutations in OsMADS13 result in the transformation of ovules into carpelloid structures, indicating its critical function in maintaining ovule identity (Dreni et al., 2007). Similarly, the comprehensive transcriptome analysis of rice female-sterile line and wild-type line ovules has identified numerous differentially expressed genes (DEGs) that are involved in ovule development and fertile female gametophyte formation, highlighting the complex regulatory networks that govern these processes (Yang et al., 2016). Additionally, microRNAs (miRNAs) have been shown to play significant roles in the regulation of ovule development in rice, further emphasizing the multifaceted nature of gene regulation in these tissues (Wu et al., 2017). 6.2 Evolutionary conservation of HAM domain genes The evolutionary conservation of HAM domain genes is evident from the functional similarities observed across different species. The rice gene OsMADS13 shares a high degree of sequence similarity with its Arabidopsis and Petunia counterparts, STK, FBP7, and FBP11, respectively. This conservation extends to their functional roles, as all these genes are involved in maintaining ovule identity (Dreni et al., 2007). The presence of conserved miRNA-mediated regulatory mechanisms during ovule development in rice also suggests an evolutionary conservation of these regulatory pathways across plant species (Wu et al., 2017). The identification of numerous DEGs associated with key metabolic and signaling pathways in rice ovules further supports the idea that these genes and their regulatory networks have been conserved through evolution to ensure proper ovule development and fertility (Yang et al., 2016). 6.3 Insights gained from cross-species comparisons Cross-species comparisons have provided valuable insights into the molecular mechanisms underlying ovule development. The functional analysis of OsMADS13 in rice has revealed its role in ovule identity and floral meristem determinacy, similar to the roles of STKin Arabidopsis and FBP7/FBP11 in Petunia (Dreni et al., 2007; Rodríguez-Cazorla et al., 2018; 2020). This cross-species functional similarity underscores the importance of these genes in reproductive development. Additionally, the transcriptome analysis of rice ovules has identified key regulatory genes and pathways that are likely conserved across species, providing a broader understanding of the genetic and molecular basis of ovule development (Yang et al., 2016). The study of miRNA expression profiles during rice ovule development has also highlighted the potential for miRNA-mediated regulation to be a conserved mechanism in plant reproductive development, offering new avenues for exploring the regulation of ovule development in other species (Wu et al., 2017; Babaei et al., 2022).
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