Characterization of Photosynthetic Pathway Genes Using Transcriptome Sequences in Drought-treated Leaves of Paulownia catalpifolia Gong Tong

Abstract

Paulownia catalpifolia Gong Tong, one of the most important fasting growing tree species in the genus Paulownia, is usually used in the production of furniture, decorative material and paper. Frequent drought and water shortage have seriously affected P. catalpifolia normal growth in recent years. Photosynthesis of plant offers both cellular energy and substrates for various biochemical reactions. However, the molecular responses of photosynthesis to drought stress are not well understood in P. catalpifolia. We sought to identify novel genes associated with photosynthesis in P. catalpifolia during drought and to construct a co-expression network for photosynthesis. The third-generation transcriptome sequencing generated 25,969 high-quality (HQ) transcripts in total, which was used as a reference sequence for this study. The RNAs from P. catalpifolia leaves collected at 0, 8 and 16 days after drought-treated were used for constructing three cDNA libraries and second-generation sequencing, approximately 199.80 million HQ clean reads were obtained and 9640 differentially expressed HQ transcripts were identified in pairwise comparisons. A total of 189 HQ transcripts related to photosynthetic pathways were identified among the 25,969 HQ transcripts, of which there were 56 high-expressing HQ transcripts in all three samples. The 40 protein families encoded by 189 HQ transcripts were classified and their expression patterns were characterized. The expression levels of most photosynthesis genes from the normal leaves were generally higher than the leaves after drought treatments, and most genes showed higher expression in the moderate-drought treatment than in the severe-drought treatment. Significantly, several genes from the leaves after drought treated were expressed more than those from normal leaves. We built a co-expression network of photosynthesis, in which we identified 94 genes with high k-core values and 13 hub genes. This work revealed a set of genes in the photosynthetic pathway that are responsive to drought stress and indicated that several genes may be critical in the drought response of P. catalpifolia.