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.
Highlights
Flowering plants have evolved a wide range of architectural features to ensure their reproductive success, including the inflorescence, which carries the flowers which later form fruits or grains
All five oil palm miRNAs belonging to the miR156/miR529/miR535 superfamily displayed a reversed accumulation profile compared with their likely targets, i.e., with higher abundance in the female inflorescence
It is interesting to note that all members of this group, which includes the rice IDEAL PLANT ARCHITECTURE1 (IPA1) protein involved in inflorescence branching, are from monocot species
Summary
Flowering plants have evolved a wide range of architectural features to ensure their reproductive success, including the inflorescence, which carries the flowers which later form fruits or grains. In the case of miR156, a role in the determination of inflorescence branching was elucidated through studies of a rice SPL gene identified through the quantitative trait loci WEALTHY FARMER’S PANICLE [10] and IDEAL PLANT ARCHITECTURE (IPA) [11]. The latter encodes the OsSPL14 protein (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 14, known as IPA1), a higher expression of which promotes panicle branching and higher grain yield. OsmiR535 is highly expressed in panicles and may be induced in response to certain abiotic stresses [14]
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