PbEIL1 acts upstream of PbCysp1 to regulate ovule senescence in seedless pear

Numerous environmental and endogenous signals control the highly orchestrated and intricate process of plant senescence. Ethylene, a well-known inducer of senescence, has long been considered a key endogenous regulator of leaf and flower senescence, but the molecular mechanism of ethylene-induced ovule senescence has not yet been elucidated. In this study, we found that blockage of fertilization caused ovule abortion in the pear cultivar ‘1913’. According to transcriptome and phytohormone content data, ethylene biosynthesis was activated by pollination. At the same time, ethylene overaccumulated in ovules, where cells were sensitive to ethylene signals in the absence of fertilization. We identified a transcription factor in the ethylene signal response, ethylene-insensitive 3-like (EIL1), as a likely participant in ovule senescence. Overexpression of PbEIL1 in tomato caused precocious onset of ovule senescence. We further found that EIL1 could directly bind to the promoter of the SENESCENCE-ASSOCIATED CYSTEINE PROTEINASE 1 (PbCysp1) gene and act upstream of senescence. Yeast one-hybrid and dual-luciferase assays revealed the interaction of the transcription factor and the promoter DNA sequence and demonstrated that PbEIL1 enhanced the action of PbCysp1. Collectively, our results provide new insights into how ethylene promotes the progression of unfertilized ovule senescence.

Transcriptomic analysis reveals ethylene signal transduction genes involved in pistil development of pumpkin

Development of female flowers is an important process that directly affects the yield of Cucubits. Little information is available on the sex determination and development of female flowers in pumpkin, a typical monoecious plant. In the present study, we used aborted and normal pistils of pumpkin for RNA-Seq analysis and determined the differentially expressed genes (DEGs) to gain insights into the molecular mechanism underlying pistil development in pumpkin. A total of 3,817 DEGs were identified, among which 1,341 were upregulated and 2,476 were downregulated. The results of transcriptome analysis were confirmed by real-time quantitative RT-PCR. KEGG enrichment analysis showed that the DEGs were significantly enriched in plant hormone signal transduction and phenylpropanoid biosynthesis pathway. Eighty-four DEGs were enriched in the plant hormone signal transduction pathway, which accounted for 12.54% of the significant DEGs, and most of them were annotated as predicted ethylene responsive or insensitive transcription factor genes. Furthermore, the expression levels of four ethylene signal transduction genes in different flower structures (female calyx, pistil, male calyx, stamen, leaf, and ovary) were investigated. The ethyleneresponsive DNA binding factor, ERDBF3, and ethylene responsive transcription factor, ERTF10, showed the highest expression in pistils and the lowest expression in stamens, and their expression levels were 78- and 162-times more than that in stamens, respectively. These results suggest that plant hormone signal transduction genes, especially ethylene signal transduction genes, play an important role in the development of pistils in pumpkin. Our study provides a theoretical basis for further understanding of the mechanism of regulation of ethylene signal transduction genes in pistil development and sex determination in pumpkin.