The effective role of CsTCP5 and CsTCP18 transcription factors from <i>Camellia sinensis</i> (L.) O. Kuntze under drought and low-temperature.

TCP transcription factors are essential for plant growth and environmental response, but little is known about their specific roles in growth, hormone response, and stress response in the tea plants. Here, CsTCP5 and CsTCP18 were cloned from the tea variety 'Longjing 43', and subcellular localization revealed that both CsTCP5 and CsTCP18 proteins were present in the nucleus. Exogenous abscisic acid (ABA) and methyl jasmonate (MeJA) had different effects on CsTCP5 and CsTCP18 expression, but both genes were repressed by drought and low-temperature treatment. Yeast-two hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays demonstrated that neither transcription factor was transcriptionally active but that each interacted with members of the CsMYB and CsJAZ families. Transgenic Arabidopsis plants overexpressing CsTCP5 had smaller cotyledons and fewer lateral roots compared with wild-type (WT) and empty vector (EV) Arabidopsis, and their root growth and germination rate were inhibited by ABA and MeJA treatment. Lateral root numbers also decreased significantly in CsTCP18-OE Arabidopsis after MeJA treatment. These results demonstrate that CsTCP5 and CsTCP18 have regulatory effects in cotyledon development, lateral root growth, and germination rate, and these effects can be modulated by ABA and MeJA. Under drought stress, the CsTCP5-OE and CsTCP18-OE lines exhibited greater survival, lower plant height, smaller rosette leaves, delayed flowering, increased activities of antioxidant enzymes, decreased MDA content, and increased proline content compared with WT and EV Arabidopsis. These findings suggest that CsTCP5 and CsTCP18 are important for tea plant growth, interact with ABA and MeJA pathways, and play roles in stress response.