USB to UART interface
No, you don't need JTAG to program the device. MSP430 also supports bootstrap loading (BSL). A special reset sequence activates the bootstrap loader, 



which uses the UART, with the following settings:


9600 bps, half duplex  
8E1 format (8 data bits, even parity, 1 stop bit


The bootstrap loader is protected with a 256-bit user defined password.  

Further reading
MSP430 Programming Via the Bootstrap Loader