English: Proteins targeting into thylakoid membranes through distinct pathways. The nuclear-encoded preprotein with an N-terminal transit peptide (TP) is translocated into the chloroplast stroma through the Toc/Tic system, and then the TP is cleaved by stromal processing peptidase. The thylakoid membrane proteins are further targeted mainly through the cpSRP pathway, cpGET pathway and the spontaneous pathway. In the cpSRP-dependent pathway, LHCP is transferred from the Toc/Tic system to the SRP43/SRP54 complex with the help of LTD., cpSRP43 interacts with the L18 region between the second and third TMD of LHCP. Then the cpSRP/LHCP complex interacts with cpFtsY and finally LHCP is insert into the thylakoid membrane by the integrase Alb3. In the cpGET pathway, imported TA proteins are transferred to the targeting factor Get3b, followed by transferr to the unknown integrases. Some proteins are translocated into thylakoid membranes spontaneously. On the other hand, the chloroplast-encoded proteins are synthesized in the stroma, and cotranslationally integrated into the thylakoid membrane with the requirement of cpSec and cpSRP components. OE, outer chloroplast envelope; IE, inner chloroplast envelope. TP, transit peptide. TMD, transmembrane domain.