Molecular strategies for prickly pear (Opuntia sp.) studies and its improvement

Nopal is a native crop from Mexico, which can grow under extreme cultivation conditions. It is an ancestral crop that helped the establishment of Mexican civilization and can contribute to the self-sufficiency and food security of Mexicans. The prickly pear (cactus fruit) shows great variability in its anatomy, which makes it attractive for marketing. However, it has two disadvantages: the high number and large size of the seeds, and the presence of the thorns. It would be of great interest to identify the underlying genetic factors of these characteristics, as to date reports on these traits are scarce or nil. The objective of this research was to generate a better understanding of the development of the fruit and its different characteristics at the molecular level, which could be applicable for possible improvement systems. Four stages of fruit development were collected: flower bud, fertilized bud, green fruit and ripe fruit of the ‘Reina’ morpho-species (with intermediate ripening behavior). The expression of microRNAs in prickly pear tissues was analyzed with microarray hybridization and by NGS transcriptome analysis. The data analysis focused on microRNAs relevant to the developmental stages of prickly pear. A total of 43 miRNAs with 26 different targets were identified from approximately 20,000 related to fruit development starting from flower induction. It highlighted the importance of miR172 and miR395, as key candidates for fruit ripening time. miR397 was also identified as a candidate for the generation of cultivars with lower seed production. The mechanism of action of the selected microRNAs was successfully tested in other plants.