Exploring the Genetic Regulation of Determinate Root Growth in Cactaceae

Most species from the Cactoideae subfamily of Cactaceae exhibit determinate growth of primary root, which implies early root apical meristem (RAM) exhaustion and cell differentiation at the root tip. This type of growth was apparently fixed after separation of the Cactiodeae/Opuntioideae from Maihuenioideae/Pereskioideae lineages (Shishkova et al., 2013). Determinate growth of the primary and lateral roots results in the formation of a compact root system that provides seedlings an advantage for survival in a desert environment. To get insight into the genetic control of the RAM exhaustion and determinate root growth in cardon Pachycereus pringlei, we employed mRNA-seq, de novo assembly of 85 nt reads with CLC Genomic Workbench and annotation by protein similarity. We analyzed differential gene expression in primary root tips in the initial growth phase (when RAM is still present), and in the terminal phase (when RAM is already exhausted). Additionally, we sequenced, grouped and annotated small RNAs differentially expressed in the root tip in the initial and terminal growth phases using small RNA analysis tools in CLC Genomics Workbench and miRBase. We also identified hundreds of novel, species-specific smRNAs that show differential expression in the two growth phases. Significant conservation was revealed for the RNA expression patterns of many genes in roots of P. pringlei and other plant species. This work was supported by PAPIIT-UNAM IN204912.