Physiological and transcriptomic responses to magnesium deficiency in Neolamarckia Cadamba

Magnesium (Mg2+) is a critical component of chlorophyll and enzymes involved in various physiological and biochemical processes essential for plant growth, biomass accumulation, and photosynthesis. Mg2+ deficiency (MgD) is common in hot and rainy subtropical areas due to its easy loss from soil. Neolamarckia cadamba, an important tropical tree in South Asia, faces severe effects of MgD, however, the responses of N. cadamba to MgD stress remain unclear. In here, effects of N. cadamba under MgD stress were investigated. The study revealed that MgD had lower plant biomass, fresh and dry weight, root length, root volume, and surface area compared to CK (normal Mg2+). As treatment time increased, the leaves began to yellow, and lesions appeared. Chlorophyll a, chlorophyll b, and total chlorophyll content, along with fluorescence-related parameters and leaf photosynthetic capacity, were significantly reduced in MgD stress compared to CK treatment. Transcriptome analysis showed that transporters as well as transcription factors (TFs) from MYC (v-myc avian myelocytomatosis viral oncogene homolog), MYB (v-myb avian myeloblastosis viral oncogene homolog), bHLH (basic helix-loop-helix) and WRKY families were upregulated in leaves at 10 d of MgD stress, indicating that magnesium signaling transduction might be activated to compensate MgD. In addition, genes including chlorophyll(ide) b reductase (NYC1/NOL) chlorophyll/bacteriochlorophyll synthase (G4) and 7-hydroxymethyl chlorophyll a reductase synthesizing (HCAR) chlorophyll a and chlorophyll b were down-regulated in leaves, while those scavenging reactive oxygen species (ROS) were mainly up-regulated at 10 d of MgD stress. These results shed light on underlying MgD in N. cadamba.