Programmed Cell Death May Be Involved in the Seedless Phenotype Formation of Oil Palm

Abstract

Oil palm (Elaeis guineensis Jacq.) is a well-known vegetable oil-yielding crop. Seedlessness is one of the most prominent traits in oil palm due to its low processing costs and high oil content. Nevertheless, an extensive study on molecular mechanisms regulating seedless phenotype formation in oil palm is very limited so far. In this study, stigma, style, and ovary from seedless and seeded (Tenera and Pisifera) oil palm trees were used to investigate the possible mechanism. Results showed that non-pollination resulted in no fruits, and self- and cross-pollinations resulted in seedless fruits, while boron treatment had no effect on seedless phenotype formation, implying that seedless trees have incomplete self and outcrossing incompatibility. Furthermore, the transcriptome data analysis highlighted eight programmed cell death (PCD) genes and three groups of PCD-related genes: 4-coumarate-CoA ligase (4CL), S-RNase, and MADS-box. The majority of these genes were significantly up-regulated in the stigma and style of Seedless palm trees compared to Tenera and Pisifera. In addition, the co-expression network analysis confirmed the significant correlation among these genes. Moreover, two simple sequence repeats (SSR) markers (S41 and S44) were developed to identify the seedless phenotype. The up-regulation of 4CL and MADS-box TFs activated the expression of PCD genes; on the other hand, S-RNase resulted in pollen tube RNA degradation and triggered PCD. While the link between PCD and seedless phenotype formation in oil palm has not been extensively studied to date, these findings suggest a role of PCD in pollen tube lethality, leading to double fertilization failure and the seedless phenotype.

Parthenocarpy-related genes induced by naphthalene acetic acid in oil palm interspecific O × G [Elaeis oleifera (Kunth) Cortés × Elaeis guineensis Jacq.] hybrids

“…Our findings agreed with the transcriptomic results published about parthenocarpy phenomena and the predicted signal pathways ( Htwe et al, 2022 ; Sharif et al, 2022 ). Critical genes such as ARF, ERF, SAUR, IAA, and GA exhibited transcriptional profiles similar to those reported previously, which implies that the oil palm O × G hybrids have similar genetic mechanisms of response to exogenously applied auxins to induce parthenocarpy ( Somyong et al, 2018 ; Htwe et al, 2022 ).…”

“…This gene has been reported in producing CoA thioesters and phenolic compounds in Arabidopsis ( Ehlting et al, 1999 ). In E. guineensis , synergic over-expression of 4CL2 and MAD-box TF activate the expression of programmed cell death genes and induce the formation of seedless phenotype ( Htwe et al, 2022 ). The exogenous application of NAA might be perceived as a chemical stress and immediately triggers a response against this stress.…”

“…The expression of genes related to the synthesis of auxins and gibberellins like EgGH3.8 (indole -3-acetic acid (IAA)-amido synthetase GH3.8), EgGH3.1 (IAA-amido synthetase GH3.1), EgARG7 (IAA induced ARG7 like), EgTAA3 (tryptophan amino transferase-related protein 3-like) and EgFMO1 (flavin-containing monooxygenase) were associated with parthenocarpic fruit development ( Somyong et al, 2018 ). On the other hand, Htwe et al (2022) studied gene expression in E. guineensis under natural pollination conditions and boron applications. Gene expression results showed eight genes associated with programmed cell death (PCD) and three groups of genes related to PCD: 4-coumarate-CoA ligase (4CL), S-RNase, and MADS-box.…”