Botanists find the molecular difference between edible pacaya and the wild palms

Pacaya palm (Chamaedorea tepejilote) is a plant eaten in Guatemala and Mexico, El Salvador, and Honduras. It’s cultivated, but not intensively. Hanene Hosni and colleagues examined how the domesticated pacaya palm differed from wild palms. They have identified molecular factors, which they think can explain why the cultivated pacaya palm grows as it does.

The pacaya palm is a dioecious palm species. Dioecious means that the plant produces just male or female flowers. For the pacaya palm, it’s the male flowers that are sought after. The male inflorescence is eaten before it matures, either cooked or raw. Over two thousand years, people have selected the best palms for breeding. Now the male palms produce larger inflorescences and have more branches, or rachillae, on them. Something has changed in how the inflorescences develop. Hosni and colleagues and colleagues wanted to understand what was going on at the molecular level to explain these changes.

The botanists harvested inflorescences from payaca palms in Guatemala and Belize. Each sample was a single inflorescence, though measuring the number of rachillae showed that the cultivated palms did have more flower spikes. At each site, they kept an eye on the local annual rainfall, altitude and soil conditions. They then sequence the RNA in the rachillae.

Why RNA and not DNA?

The answer is because the team weren’t looking at the genes but rather what the genes were doing. To get from DNA to the proteins in plants, there’s an intermediate step where RNA takes the information from the DNA. Not every gene will produce material in a plant. Only some genes are expressed, so, by looking at the RNA, the scientists could look at what processes were active in the cells.

The team found three categories of genes that showed differences in expression activity: redox, transport and secondary metabolism. “Transport-related genes encode proteins involved in the movement across cell membranes of a wide range of molecules, both ionic and organic,” write Hosni and colleagues. “Concerning the latter type, it is interesting to note that three different palm transport-related genes are more highly expressed in the cultivated morphotype, namely those encoding respectively a SWEET1-type protein, a hexose carrier protein and a polyol transporter, all of which are known to influence sugar accumulation…”

“Pacaya palms of the cultivated morphotype produce inflorescences that are larger in size than their wild relatives, with a higher degree of branching (averaging over 3 times as many rachillae). This implies that at the earliest stages of development, the expression of certain developmentally important genes is different in the cultivated and wild morphotypes. The plant material analysed in this study was harvested at a relatively late stage of inflorescence development, after the period when the basic architecture is determined… Nevertheless, given the enrichment of redox- related genes observed in the C_up DEG set, it is interesting to note that a link has been established between redox balance and the regulation of certain developmental processes in plants.” One example the team give is bud outgrowth, referring to earlier work on grapevine and roses.

While there’s no vast demand for pacaya, it is a valuable plant to study, thanks to its relatives, say Hosni and colleagues. “Although pacaya is of only minor importance as a food crop on a world scale and is little known outside Latin America, it provides an interesting case study to extend the large body of data obtained on the inflorescence of crop plants, especially cereals, to another key monocot group.”