In-Depth Understanding of Camellia oleifera Self-Incompatibility by Comparative Transcriptome, Proteome and Metabolome

Abstract

Oil-tea tree (Camellia oleifera) is the most important edible oil tree species in China with late-acting self-incompatibility (LSI) properties. The mechanism of LSI is uncertain, which seriously hinders the research on its genetic characteristics, construction of genetic map, selection of cross breeding parents and cultivar arrangement. To gain insights into the LSI mechanism, we performed cytological, transcriptomic, proteomic and metabolomic studies on self- and cross-pollinated pistils. The studies identified 166,591 transcripts, 6851 proteins and 6455 metabolites. Transcriptomic analysis revealed 1197 differentially expressed transcripts between self- and cross-pollinated pistils and 47 programmed cell death (PCD)-control transcripts. Trend analysis by Pearson correlation categorized nine trend graphs linked to 226 differentially expressed proteins and 38 differentially expressed metabolites. Functional enrichment analysis revealed that the LSI was closely associated with PCD-related genes, mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, ATP-binding cassette (ABC) transporters and ubiquitin-mediated proteolysis. These particular trends in transcripts, proteins and metabolites suggested the involvement of PCD in LSI. The results provide a solid genetic foundation for elucidating the regulatory network of PCD-mediated self-incompatibility in C. oleifera.

CoNPR1 and CoNPR3.1 are involved in SA‐ and MeSA‐ mediated growth of the pollen tube in Camellia oleifera

“…The pollen tubes of Yali pear grow rapidly on the second day after pollination, and the content of SA in the pollinated pistils increases at the same time (Zhao, 2004). Similar result in this study was that the content of SA and MeSA increased at 0–24 h after self‐ or cross‐pollination (Figure 1A,B), when the pollen tubes grow in the style (Gao et al, 2015; Liao et al, 2014; Zhou et al, 2020). In addition, both SA and MeSA inhibited pollen germination and pollen tube elongation at higher concentrations (Figure 1C–F).…”

“…Upon analysis of the transcriptome database of C. oleifera (Zhou et al, 2020), four differential NPR1‐like genes were found. They were named CoNPR1 , CoNPR3.1 , CoNPR3.2 , and CoNPR5 , respectively, and their CDS sequences and gDNA sequences were cloned by RT‐PCR (Figure 2).…”

“…Furthermore, CoNPR1 and CoNPR3.1 had relatively high expression levels in pollen tubes (Figure 4A,B) and their expression levels in pollen tubes were regulated by SA and MeSA, which were basically consistent with the trend of pollen germination (Figure 6, Figure 1C and E). The expression levels of CoNPR1 increased at 0–24 h after self‐ or cross‐ pollination (Figure 1A,B), when the pollen tubes grow in the style (Gao et al, 2015; Liao et al, 2014; Zhou et al, 2020). It can be speculated that CoNPR1 and CoNPR3.1 may be directly involved in pollen germination and pollen tube growth.…”

“…The plant hormone signal transduction pathway is significantly enriched in pear (Shi et al, 2017) and “Xiangshui” lemon (Zhang et al, 2015), with gametophytic self‐incompatibility (GSI) properties, as well as in oil‐tea tree (Zhou et al, 2020) and tea plant (Zhang, Jiao, et al, 2016; Zhang, Wang, et al, 2016) with LSI properties, implying that plant hormone signals play an indispensable role in plant self‐incompatibility (SI) responses. The contents of indole‐3‐acetic acid (IAA), zeatin (ZT), and gibberellic acid (GA) in the cross‐pollinated ovaries of Shatian pomelo are significantly higher than in self‐pollinated ovaries, while abscisic acid (ABA) exhibits the opposite response (Qin et al, 1998).…”

Comparative study on fruit development and oil synthesis in two cultivars of Camellia oleifera

“…A total 24 samples were rapidly frozen in liquid nitrogen and stored at -80 °C. The purity, concentration, and integrity of the RNA samples were assessed using agarose gel electrophoreses and the Nanodrop 2500 instrument (Thermo Fisher Scientific, USA) to ensure that they were suitable for transcriptome sequencing [ 4 , 31 ].…”