Comparison of phytohormone biosynthesis and signal transduction pathways in developing and abortive hazelnut ovules

Abstract

In hazelnuts, ovule abortion is associated with the formation of empty nuts, resulting in serious yield losses. Phytohormones play important roles in plant growth and development; however, the mechanisms through which they regulate ovule abortion in hazelnut are largely unknown. RNA-seq identified 1209 differentially expressed genes with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation between developing and abortive ovules in hazelnut. Hormone signal transduction (ko04075), and several phytohormone biosynthesis pathways, were found to be significantly enriched after pathway enrichment analysis. Compared with developing ovules, the levels of indole-3-acetic acid (IAA), gibberellins (GA), cytokinin (CTK), and salicylic acid (SA) were found to be significantly lower in abortive ovules, while levels of abscisic acid (ABA), ethylene (ETH), and jasmonic acid (JA) were found to be significantly higher. Consistent with these results, some important rate-limiting enzymes involved in the biosynthesis of phytohormones, including 9-cis-epoxycarotenoid dioxygenase, ACC synthase, and phospholipase A1 were significantly up-regulated in abortive ovules. Some key genes in the ETH, JA, and ABA signal transduction pathways were highly upregulated, including ethylene-responsive transcription factor 1 (ERF1/2) and the serine/threonine-protein kinase CTR1 in the ETH signal pathway, jasmonate ZIM domain-containing protein (JAZ) and the transcription factor MYC2 in the JA signal pathway, and ABA responsive element binding factor (ABF) in the JA signal pathway. Thus, ABA, ETH, and JA signaling were more active in abortive ovules than in developing ovules. Expression levels of NCED, ABF, ACS, ERF1/2, PLA1, and MYC2 revealed by q-RT-PCR were consistent with the results obtained by differentially expressed genes (DEG) analysis. Our data suggest that multiple phytohormone signaling pathways are involved in the development of hazelnut ovules. Inhibition of IAA, GA, CTK, and SA biosynthesis and signaling pathways, and activation of ABA, ETH, and JA biosynthesis and signaling pathways may contribute to the formation of abortive ovules in hazelnut.