Micro-RNA-Regulated SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) Gene Expression and Cytokinin Accumulation Distinguish Early-Developing Male and Female Inflorescences in Oil Palm (Elaeis guineensis)

Abstract

Sexual differentiation of inflorescences and flowers is important for reproduction and affects crop plant productivity. We report here on a molecular study of the process of sexual differentiation in the immature inflorescence of oil palm (Elaeis guineensis). This species is monoecious and exhibits gender diphasy, producing male and female inflorescences separately on the same plant in alternation. Three main approaches were used: small RNA-seq to characterise and study the expression of miRNA genes; RNA-seq to monitor mRNA accumulation patterns; hormone quantification to assess the role of cytokinins and auxins in inflorescence differentiation. Our study allowed the characterisation of 30 previously unreported palm MIRNA genes. In differential gene and miRNA expression studies, we identified a number of key developmental genes and miRNA-mRNA target modules previously described in relation to their developmental regulatory role in the cereal panicle, notably the miR156/529/535-SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) gene regulatory module. Gene enrichment analysis highlighted the importance of hormone-related genes, and this observation was corroborated by the detection of much higher levels of cytokinins in the female inflorescence. Our data illustrate the importance of branching regulation within the developmental window studied, during which the female inflorescence, unlike its male counterpart, produces flower clusters on new successive axes by sympodial growth.

Convergent evolution of sex chromosomes in palms

“…The gene squamosa promoter-binding-like protein_6 (SPL6) (LOC103724287) in K. elegans is homologous to SPL8 in Arabidopsis thaliana, involved in anther development and male fertility (30). Additionally, the sex-linked transcription factor phytochrome interacting factor-like 15 (PIL) (LOC103697220) in K. elegans is similar to PIL family factors that interact with SPLs (31) and is orthologous to the oil palm LOC105059744 gene that displays sex-dependent expression (32). All the sexlinked genes mentioned have homologs positioned in the 43 and 46.1Mb region of the E. guineensis chromosome 10, except the LOG3 gene located in the chromosome 12 (Table 1).…”

Influence of cultivation practices on the metabolism of cytokinin and its correlation in rice production

“…CTK also has an important regulatory effect on grain storage capacity (library strength) (Chen et al, 2019). During development of the floral organ meristem, an increase in CTK concentration or an increase in CTK signaling pathway activity promotes cell division and differentiation of the floral organ meristem, thereby increasing the number of reproductive organs (Tregear et al, 2022). A reduction in the activity of CTK oxidase CKX can increase the CTK content and increase the storage capacity of the grain.…”

The Role of Noncoding RNAs in the Response of Oil Palm Plants to Abiotic Stresses

“…Despite many advancements in the prediction and characterization of miRNAs in plants, there are only a few studies where researchers report the identification and characterization of miRNAs in oil palm, either under abiotic stress conditions or not. Currently, there are 10 published studies reporting miRNAs identification and characterization in oil palm [15,30,[56][57][58][59][60][61][62][63]. Considering the great economic importance of oil palm, the number of miRNA studies reported on this oilseed crop is relatively low (Table 1).…”

“…They found 37 fatty acid synthesis-related genes as putative miRNA-target genes and indicated that 22 conserved miRNAs and 14 new ones might be involved in fatty acid metabolism pathways. Tregear et al [63] reported finding 30 previously unreported oil palm miRNA genes in a molecular study of the process of sexual differentiation in the immature inflorescence of oil palm.…”