Genomics and Applied Biology 2024, Vol.15, No.4, 200-211 http://bioscipublisher.com/index.php/gab 208 8.3 Challenges and prospects in R2R3-MYB gene research Despite the promising potential of R2R3-MYB genes in rice improvement, several challenges remain. One significant challenge is the functional redundancy and intricate regulatory networks involving multiple MYB genes, which render the elucidation of their specific roles a complex undertaking. Furthermore, the co-evolutionary patterns observed between different domains of R2R3-MYB proteins indicate the presence of intricate protein-DNA and protein-protein interactions that require comprehensive investigation. It is recommended that future research employ integrative approaches combining genomics, transcriptomics, proteomics, metabolomics, and phenomics to unravel the complex regulatory mechanisms of R2R3-MYB genes (Chen et al., 2022; Gupta et al., 2023; Xiong et al., 2022; Zhang et al., 2023; Zhang et al., 2022; Zhao et al., 2024). Furthermore, the advent of sophisticated gene editing techniques, such as CRISPR/Cas9, presents a promising avenue for precise manipulation of MYB genes to achieve desired phenotypic outcomes in rice (Dai et al., 2007; Biswal et al., 2019). 9 Concluding Remarks This systematic review has comprehensively identified and characterized the R2R3-MYB gene family in rice, thereby providing significant insights into their evolutionary relationships, structural features, and expression profiles. Notable findings include the distinctive structural characteristics of R2R3-MYB genes in colored rice, such as elevated frequencies of non-synonymous substitutions in the DNA-binding domains, particularly in the α-helix regions. This suggests adaptive selection and functional diversification. The expression patterns of R2R3-MYB genes were found to be tissue-specific and developmentally regulated, with genes within certain clades predominantly expressed in specific tissues, such as leaves and roots. This suggests that they may have specialized roles in photosynthesis-related processes and root development, respectively. Moreover, R2R3-MYB genes were identified as pivotal regulators of anthocyanin biosynthesis. Genes such as OsC1 and OsKala3 were found to play a pivotal role in modulating the expression of anthocyanin biosynthetic pathway genes, underscoring their significance in conferring the distinctive purple pigmentation and associated health benefits observed in purple rice. The findings from this study have significant implications for the breeding of colored rice. The identification of unique allelic variations and key regulatory genes provides valuable genetic resources that can be utilized to enhance desirable traits such as disease resistance, stress tolerance, and nutritional value. The functional characterization of R2R3-MYB genes, such as OsMYB2P-1 and OsMYB103L, offers potential targets for genetic engineering to improve traits like leaf morphology and pericarp pigmentation, which are important for both agronomic performance and consumer preference. The use of advanced genomic tools, such as CRISPR/Cas9, can further facilitate the precise editing of these genes to achieve targeted improvements in grain yield and other agronomically important traits. The broader impact of this research extends beyond the specific topic of colored rice to the wider field of plant science and agriculture. The insights gained into the genetic architecture and regulatory mechanisms of R2R3-MYB genes can inform the breeding and genetic engineering of other crop species, thereby contributing to global food security and agricultural sustainability. The study also highlights the necessity of conserving and employing genetic diversity in crop improvement programs, as evidenced by the extensive allelic diversity observed in the Purpleputtu rice landrace. Moreover, the public accessibility of genomic data from extensive initiatives, such as the 3 000 Rice Genomes Project, offers a significant asset for continuous research and breeding endeavors aimed at improving crop performance and resilience. Acknowledgments We appreciate the anonymous peer reviewers for their revision suggestions on the manuscript. Funding This work was supported by the Scientific Research Foundation of Panxi Crops Research and Utilization Key Laboratory of Sichuan
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