RNA sequencing analysis of low temperature and low light intensity-responsive transcriptomes of zucchini (Cucurbita pepo L.)

Zucchini seedlings are commonly subjected to low temperatures and low light densities, which are environmental factors that severely impair plant growth and agricultural production. Little is known, however, about the molecular mechanisms regulating responses to these conditions. In this study, we sequenced a zucchini transcriptome after merging data from untreated control and from plants exposed to low temperature (4 °C) or low light intensity (80 μmol photons m―2 s―1. A total of 234,583 transcripts N50 = 2609 bp were generated, and 83,650 unigenes N50 = 1257 bp were predicted. Under low-temperature conditions, 982 and 340 genes were up- and down-regulated, respectively. Fewer genes were up- 834 and down-regulated 216 under low light intensity stress, indicating that the zucchini seedlings were more sensitive to the applied low temperature than the low light intensity stress. Functional enrichment analyses identified many common or specific biological processes and gene sets responsive to low temperature and low light intensity. In addition, 18 full-length cDNA genes from six gene families (LHCB, POD, SOD, ABAR, ICE1, and COR) and five transcription factor families (AP2/ERF, NAC, ZFP, WRKY, and MYB) identified as potentially associated with both stresses were observed to be differentially expressed in zucchini leaves. Furthermore, KEGG pathway analysis uncovered many important pathways, including those related to plant hormone signal transduction, starch and sucrose metabolism, and phenylpropanoid biosynthesis. We also confirmed the expressions of these unigenes by quantitative real-time polymerase chain reaction analysis. Our findings and the identified functional genes can provide useful clues for improving the abiotic stress tolerance of zucchini by exploitation of the underlying mechanisms.