curl: (60) SSL certificate problem: unable to get local issuer certificate

[ShuqingL]

I install EDirect correctly, and add the edirect directory path to $PATH.
When I test it(eg: esearch -db pubmed -query "Babalobi OO[au] AND 2008[pdat]" ), I got error like below:

curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: http://curl.haxx.se/docs/sslcerts.html

curl performs SSL certificate verification by default, using a "bundle"
of Certificate Authority (CA) public keys (CA certs). If the default
bundle file isn't adequate, you can specify an alternate file
using the --cacert option.
If this HTTPS server uses a certificate signed by a CA represented in
the bundle, the certificate verification probably failed due to a
problem with the certificate (it might be expired, or the name might
not match the domain name in the URL).
If you'd like to turn off curl's verification of the certificate, use
the -k (or --insecure) option.