The plant vacuolar sorting receptor AtELP is involved in transport of NH2-terminal propeptide-containing vacuolar proteins in Arabidopsis thaliana

Many soluble plant vacuolar proteins are sorted away from secreted proteins into small vesicles at the trans-Golgi network by transmembrane cargo rece ptors. Cleavable vacuolar sorting signals include the NH2-terminal propepti de (NTPP) present in sweet potato sporamin (Spo) and the COOH-terminal prop eptide (CTPP) present in barley lectin (BL),These two proteins have been fo und to be transported by different mechanisms to the vacuole. We examined t he ability of the vacuolar cargo receptor AtELP to interact with the sortin g signals of heterologous and endogenous plant vacuolar proteins in mediati ng vacuolar transport in Arabidopsis thaliana. AtELP extracted from microso mes was found to interact with the NTPPs of barley aleurain and Spo, but no t with the CTPPs of BL or tobacco chitinase, in a pi-I-dependent and sequen ces-specific manner. In addition, EM studies revealed the colocalization of AtELP with NTPP-Spo at the Golgi apparatus, but not with BL-CTPP in roots of transgenic Arabidopsis plants. Further, we found that AtELP interacts in a similar manner with the NTPP of the endogenous vacuolar protein AtALEU ( Arabidopsis thaliana Aleu), a protein highly homologous to barley aleurain, We hypothesize that AtELP functions as a vacuolar sorting receptor involve d in the targeting of NTPP-, but not CTPP-containing proteins in Arabidopsi s.