Genomics and Applied Biology 2024, Vol.15, No.6, 320-332 http://bioscipublisher.com/index.php/gab 327 Furthermore, the study used transcriptome and weighted gene co-expression network analysis (WGCNA) to reveal regulatory networks between genes and transcription factors involved in betalain biosynthesis. The results showed that betalains (betacyanin and betaxanthin) gradually increased in the pulp of 'GHH' and were significantly higher compared to 'GHB'. Betalain biosynthesis-related genes such as ADH, CYP76AD1, and DODAwere highly expressed during the maturation of GHH pulp, indicating that their high expression is directly related to betalain accumulation, highlighting the crucial role of gene expression in fruit color changes (Figure 4). This research provides valuable genomic resources for the molecular breeding of pitaya and offers new insights into understanding pitaya genome evolution and betalain regulation. Figure 3 Indeterminate and determinate root growth (Adopted from Rodriguez-Alonso et al., 2018) Image caption: (a) Growing roots can be divided in three developmental zones along the longitudinal axis as illustrated here for the Arabidopsis thaliana primary root; the root apical meristem (RAM) is located in the meristematic zone and it is present and active in most angiosperm roots for long periods. (b) The developmental zones in an A. thaliana lateral root can be distinguished by the cell features. Scale bar: 100 µm. (c) The RAM contains a quiescent centre composed of cells with very low mitotic rate (white cells in the scheme). The cells adjacent to the quiescent centre, delimited with a thick line, are called stem (initial) cells, and are a source of the dividing cells for the meristem. (d–f) The Pachycereus pringlei primary root exhibits determinate growth. In this work, 1 mm of the primary root apex, delimited with a white or black box, was collected at three developmental stages: initial, when the RAM is present and fully active (d); intermediate, when the RAM is smaller and the differentiation zone is closer to the root apex (e); and terminal, when the RAM is exhausted and all the cells in the root, including those at the root apex, are differentiated (f). A mature P. pringlei is shown in (g). (a) and (c) were taken and modified from Peret, Benjamin (2017): doi:10.6084/m9.figshare.5143987.v4, originally deposited on FigShare as open access content under a CC BY 4.0 license (Adopted from Rodriguez-Alonso et al., 2018) 7 Challenges and Future Directions in Cactaceae Breeding 7.1 Limitations of current breeding techniques The genetic improvement of Cactaceae is often limited by the biological characteristics of these plants, including their slow growth rates, long generation times, and complex reproductive mechanisms. Traditional breeding methods, such as hybridization and selection, are labor-intensive and time-consuming, which makes significant progress difficult to achieve within a reasonable timeframe (Khan et al., 2019; Ramanauskas and Igić, 2021). Cacti exhibit a high degree of genetic diversity, which, while beneficial for resilience, poses challenges for achieving consistency in desired traits across cultivars (Da Silva et al., 2021). Moreover, the incompatibility between species and the occurrence of polyploidy in certain Cactaceae often complicate crossbreeding efforts. The chromosomal analysis of Pachycereus pringlei indicates that polyploidy (tetraploid) is widely distributed, affecting its reproductive isolation and breeding system (Gutiérrez-Flores et al.,
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