Bioscience Evidence 2024, Vol.14, No.5, 218-226 http://bioscipublisher.com/index.php/be 219 of the molecular events involved. This knowledge can contribute to the development of strategies for improving rice fertility and yield through genetic and biotechnological approaches. 2 The Role of HAM Domain Genes in Plant Development 2.1 General functions of HAM domain genes HAM domain genes, part of the GRAS family of transcriptional regulators, play crucial roles in the development and maintenance of shoot apical meristems (SAMs) in land plants. These genes are essential for the initiation and proliferation of stem cells within the SAM, which are responsible for the continuous formation of aboveground plant organs. The HAM family members are involved in dictating shoot stem cell initiation and proliferation, and their expression domains are shaped by specific signaling cascades (Geng and Zhou, 2021a; Geng et al., 2021). The N-terminal regions of HAM proteins, although variable and divergent, are important for their conserved functions across different plant lineages (Geng and Zhou, 2021b). 2.2 HAM domain genes in other plant species The HAM domain genes are conserved across various plant species, including angiosperms, bryophytes, lycophytes, ferns, and gymnosperms. This conservation suggests that HAM genes originated before the divergence of bryophytes. In angiosperms, HAM genes have duplicated into two distinct groups, Type I and Type II, with Type II being widely present. Interestingly, HAM genes from non-angiosperms can replace the function of Type II HAM genes in Arabidopsis, indicating their conserved role in maintaining SAMs and promoting new stem cell niches (Geng et al., 2021). In Brassica napus, a genome-wide survey revealed the presence of 87 GRAS genes, including HAM subfamily members, which are involved in root development and stress response (Guo et al., 2019). In litchi, the GRAS gene family, including HAM subfamily members, plays roles in seed development and is regulated by miR171-mediated degradation (Figure 1) (Chen et al., 2021). Figure 1 Target plots (t-plots) of identified miR171 targets in litchi using degradome sequencing (Adopted from Chen et al., 2021) Image caption: T-plots from degradome data were shown in each panel, red lines indicate signatures consistent with miRNA-directed cleavage. The red vertical arrows point to the predicted cleavage sites. P: P-vaule. The yellow and pink color indicate the CDS region and the GRAS domain of the gene, respectively (Adopted from Chen et al., 2021)
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