Long-term cold, freezing and drought: overlapping and specific regulatory mechanisms and signal transduction in tea plant ( (L.) Kuntze).

INTRODUCTION

Low temperatures and drought are two main environmental constraints reducing the yield and geographical distribution of horticultural crops worldwide. Understanding the genetic crosstalk between stress responses has potential importance for crop improvement.

METHODS

In this study, Illumina RNA-seq and Pac-Bio genome resequencing were used to annotate genes and analyze transcriptome dynamics in tea plants under long-term cold, freezing, and drought.

RESULTS

The highest number of differentially expressed genes (DEGs) was identified under long-term cold (7,896) and freezing (7,915), with 3,532 and 3,780 upregulated genes, respectively. The lowest number of DEGs was observed under 3-day drought (47) and 9-day drought (220), with five and 112 genes upregulated, respectively. The recovery after the cold had 6.5 times greater DEG numbers as compared to the drought recovery. Only 17.9% of cold-induced genes were upregulated by drought. In total, 1,492 transcription factor genes related to 57 families were identified. However, only 20 transcription factor genes were commonly upregulated by cold, freezing, and drought. Among the 232 common upregulated DEGs, most were related to signal transduction, cell wall remodeling, and lipid metabolism. Co-expression analysis and network reconstruction showed 19 genes with the highest co-expression connectivity: seven genes are related to cell wall remodeling (, , , , , , and ), four genes are related to calcium-signaling (, , , and ), three genes are related to photo-perception (, , and ), two genes are related to hormone signaling ( and ), two genes are involved in ROS signaling ( and ), and one gene is related to the phenylpropanoid pathway ().

DISCUSSION

Based on our results, several important overlapping mechanisms of long-term stress responses include cell wall remodeling through lignin biosynthesis, o-acetylation of polysaccharides, pectin biosynthesis and branching, and xyloglucan and arabinogalactan biosynthesis. This study provides new insight into long-term stress responses in woody crops, and a set of new target candidate genes were identified for molecular breeding aimed at tolerance to abiotic stresses.