Multidimensional analysis of the effects of drought stress on chlorophyll synthesis in Lonicera japonica leaves

Abstract Background Lonicera japonica is an important medicinal plant, and its drought resistance is often related to the yield and the economic income of farmers. The drought resistance of plants is closely related to the mechanism of chlorophyll synthesis and decomposition. At present, many scientific reports have focused on the effects of drought stress on photosynthesis and chlorophyll content of L. japonica, but have not studied the chlorophyll anabolism of L. japonica from the perspective of molecular mechanism and metabolic level. Results To analyze the response mechanism of chlorophyll synthesis in honeysuckle (Lonicera japonica) plants under drought stress and to screen for the key regulatory genes and precursor metabolites associated with chlorophyll synthesis, a control group (CK) and three experimental groups, which were subjected to light stress (L), moderate stress (M), or severe stress (S), were established in this study. The mechanism of chlorophyll synthesis in L. japonica leaves under drought stress was comprehensively analyzed at the physiological, biochemical, transcriptional, and metabolic levels. Physiological and biochemical studies revealed that with increasing drought stress, the total chlorophyll content (Ct) of L. japonica leaves tended to initially exhibit a slight increase and then a sharp decrease, and the content of most chlorophyll synthesis-related enzymes decreased. A total of 37,735 differential genes (DEGs) were identified by transcriptome analysis, 16 of which were related to chlorophyll synthesis. Metabolomic analysis revealed a total of 2,132 differentially abundant metabolites, 4 of which were precursors of differentially accumulated substances in the chlorophyll synthesis pathway. Conclusions The multidimensional analysis results show that the metabolite Mg-protoporphyrin IX monomethyl ester and the closely related gene HEMA1 may be key precursors of chlorophyll synthesis and key regulators of chlorophyll synthesis in L. japonica during drought stress. However, the mechanism of the influence of HEMA1 and Mg-protoporphyrin IX monomethyl ester on chlorophyll synthesis under drought stress has yet to be explored. This study is highly important for furthering the understanding of drought resistance mechanisms in medicinal plants and for molecular breeding to produce new varieties of honeysuckle with strong drought tolerance.