Pseudophoenix ekmanii (Arecaceae) seeds at suboptimal temperature show reduced imbibition rates and enhanced expression of genes related to germination inhibition

Abstract

Pseudophoenix ekmanii is a critically endangered palm species that can be found in the southeast of the Dominican Republic. The temperatures to which P. ekmanii seeds are exposed upon dispersal range from 32 to 23 °C (max and min) and can reach a low of approximately 20 °C in January. Our aim was to analyse the effect of suboptimal (20 °C) and optimal (30 °C) germination temperature on seed imbibition, moisture content, embryo growth and gene expression patterns in this tropical palm species. Seed imbibition was tracked using whole seeds, while moisture content was assessed for individual seed sections. Embryo and whole seed size were measured before and after full imbibition. For transcriptome sequencing, mRNA was extracted from embryo tissues only and the resulting reads were mapped against the Elaeis guineensis reference genome. Differentially expressed genes were identified after statistical analysis and subsequently probed for enrichment of Gene Ontology categories ‘Biological process’ and ‘Cellular component’. Our results show that prolonged exposure to 20 °C slows whole seed and embryo imbibition and causes germination to be both delayed and inhibited. Embryonic transcriptome patterns associated with the negative regulation of germination by suboptimal temperature include up‐regulation of ABA biosynthesis genes, ABA‐responsive genes, as well as other genes previously related to physiological dormancy and inhibition of germination. Thus, our manuscript provides the first insights into the gene expression patterns involved in the response to suboptimal temperature during seed imbibition in a tropical palm species.

Ecological insights into the coexistence of dormancy and desiccation-sensitivity in Arecaceae species

“…One possible reason for the presence of dormancy in desiccation-sensitive Arecaceae seeds can be ascribed to the fact that a wet soil surface alone does not ensure germination success. Seeds also have a hightemperature requirement (c. 25-40 °C, with 30 °C being optimal for many species) to germinate, and this temperature range occurs in the tropical rainforest all year (Broschat 1998;Hussey 1958;Rees 1962;Visscher et al 2020). However, soil temperature increasing to 40-60 °C is a common occurrence, and such "erratic" high temperatures on the soil surface have a risk of drying the seeds.…”

Seed Transcriptome Annotation Reveals Enhanced Expression of Genes Related to ROS Homeostasis and Ethylene Metabolism at Alternating Temperatures in Wild Cardoon

“…To date, transcriptome investigation has been scarcely applied in seed physiology since it was considered to provide only a partial understanding of the cellular events regulating seed dormancy alleviation or termination processes [ 27 , 28 ]. However, many recent contributions showed that, especially for species for which there is a lack of molecular data, transcripts composition analysis provides new insights on gene interactions and their regulatory mechanisms [ 29 , 30 , 31 ]. Microarray analysis showed that thermal oscillations elicited almost immediate large transcriptome changes in leafy spurge seeds exposed to alternating temperatures [ 5 , 32 ].…”

Defining correct dormancy class matters: morphological and morphophysiological dormancy in Arecaceae

“…With 2600+ species, palms constitute an essential component of tropical and sub-tropical biodiversity (Kissling et al 2019). The life cycle of long-lived palms starts with diaspores, which differ considerably in size, shape, and color (Broschat et al 2014;Corner 1966;Mabberley 2017;Tomlinson 1990). Typically, the dispersal unit of palms is a berry or fibrous drupe, which encompasses fibrous mesocarp, a thick endocarp, a fleshy nutritious endosperm, and a small embryo (Tomlinson 1990).…”

“…The life cycle of long-lived palms starts with diaspores, which differ considerably in size, shape, and color (Broschat et al 2014;Corner 1966;Mabberley 2017;Tomlinson 1990). Typically, the dispersal unit of palms is a berry or fibrous drupe, which encompasses fibrous mesocarp, a thick endocarp, a fleshy nutritious endosperm, and a small embryo (Tomlinson 1990). It is well known (or inferred) that mostperhaps all-palm diaspores have an underdeveloped embryo, c. > 10% of the overall diaspore size, at the time of dispersal (Baskin and Baskin 2014b;Martin 1946;Tomlinson 1990).…”

“…Typically, the dispersal unit of palms is a berry or fibrous drupe, which encompasses fibrous mesocarp, a thick endocarp, a fleshy nutritious endosperm, and a small embryo (Tomlinson 1990). It is well known (or inferred) that mostperhaps all-palm diaspores have an underdeveloped embryo, c. > 10% of the overall diaspore size, at the time of dispersal (Baskin and Baskin 2014b;Martin 1946;Tomlinson 1990). This feature-termed as morphological dormancy-means that embryos require time for the embryo to differentiate and grow inside the diaspores before germination occurs, which is usually within 30 days after dispersal (Baskin and Baskin 2004;Finch-Savage and Leubner-Metzger 2006;Nikolaeva 1969; see Fig.…”