Transcriptome Analysis of Cell Wall and NAC Domain Transcription Factor Genes during Elaeis guineensis Fruit Ripening: Evidence for Widespread Conservation within Monocot and Eudicot Lineages

Abstract

The oil palm (Elaeis guineensis), a monocotyledonous species in the family Arecaceae, has an extraordinarily oil rich fleshy mesocarp, and presents an original model to examine the ripening processes and regulation in this particular monocot fruit. Histochemical analysis and cell parameter measurements revealed cell wall and middle lamella expansion and degradation during ripening and in response to ethylene. Cell wall related transcript profiles suggest a transition from synthesis to degradation is under transcriptional control during ripening, in particular a switch from cellulose, hemicellulose, and pectin synthesis to hydrolysis and degradation. The data provide evidence for the transcriptional activation of expansin, polygalacturonase, mannosidase, beta-galactosidase, and xyloglucan endotransglucosylase/hydrolase proteins in the ripening oil palm mesocarp, suggesting widespread conservation of these activities during ripening for monocotyledonous and eudicotyledonous fruit types. Profiling of the most abundant oil palm polygalacturonase (EgPG4) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) transcripts during development and in response to ethylene demonstrated both are sensitive markers of ethylene production and inducible gene expression during mesocarp ripening, and provide evidence for a conserved regulatory module between ethylene and cell wall pectin degradation. A comprehensive analysis of NAC transcription factors confirmed at least 10 transcripts from diverse NAC domain clades are expressed in the mesocarp during ripening, four of which are induced by ethylene treatment, with the two most inducible (EgNAC6 and EgNAC7) phylogenetically similar to the tomato NAC-NOR master-ripening regulator. Overall, the results provide evidence that despite the phylogenetic distance of the oil palm within the family Arecaceae from the most extensively studied monocot banana fruit, it appears ripening of divergent monocot and eudicot fruit lineages are regulated by evolutionarily conserved molecular physiological processes.

Genome-wide analysis of the NAC transcription factor family and their expression during the development and ripening of the Fragaria × ananassa fruits

“…This approach has revealed functions to NAC proteins in several plants, such those implied in salt stress in Cucumis melo [ 62 ], drought responses in maize [ 63 ], abiotic stresses and stress-related phytohormone treatments in Brachypodium distachyon [ 64 ] and ethylene-responsive signaling in banana [ 22 ]. Other studies have assigned a wider range of functions to the NAC proteins using the same approach [ 52 , 65 , 66 , 67 , 68 ]. Thus, we run a Clustal Omega alignment with all NAC protein sequences from Arabidopsis along the six developmental and ripening related NAC TFs from strawberry to predict their functions.…”

Single berry sampling reveals novel insights into transcriptomic changes induced by leafroll virus infections in grapevine (V. vinifera)

“…The NAC family has been characterized in a number of plant species that comprise a conserved NAM domain in the N-terminus. NAC transcription factors have been shown to participate in diverse biological processes, including hormone signaling [105][106][107], leaf senescence [108][109][110][111], secondary cell wall development and components [112][113][114][115] and have been reported to be involved in regulating plant development at different growth stages [116][117][118][119][120][121][122][123][124][125]. Interestingly, VvNAC60…”

Genome-Wide Identification and Characterization of the NAC Transcription Factor Family in Musa Acuminata and Expression Analysis during Fruit Ripening

“…Among numerous TFs, NAC (NAM, ATAF, CUC2) proteins constitute one of the largest plant-specific transcription factor gene families [5], with 105 in Arabidopsis [6], 140 in rice [7], 152 in soybean [8], 163 in Populus trichocarpa [9], and 180 in apple [10]. The N-terminus of the NAC domain is conserved while the C-terminus is highly divergent, which is responsible for the transcriptional activation involved in various processes such as developmental programs [11][12][13][14][15], defense [16,17], and responses to abiotic stress [17][18][19][20], among others. NAC TFs have been shown to exhibit important effects in ethylene biosynthesis, reception, and signaling during the fruit ripening of tomato [12].…”