<PAGE>


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549
                           --------------------------

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       The Securities Exchange Act of 1934
                            -------------------------

       Date of Report (Date of earliest event reported): December 15, 2005

                          MERRILL LYNCH DEPOSITOR, INC.
                 (ON BEHALF OF PREFERREDPLUS TRUST SERIES UPC-1)
             (Exact name of registrant as specified in its charter)

       DELAWARE                 001-31484                    13-3891329
   (State or other            (Commission                (I. R. S. Employer
   jurisdiction  of            File Number)              Identification No.)
    incorporation)

         WORLD FINANCIAL CENTER,                       10080
           NEW YORK, NEW YORK                       (Zip Code)
          (Address of principal
           executive offices)

                           --------------------------

       Registrant's telephone number, including area code: (212) 449-1000

                      INFORMATION TO BE INCLUDED IN REPORT


SECTION 1. REGISTRANT'S BUSINESS AND OPERATIONS

           Not applicable.

SECTION 2. FINANCIAL INFORMATION

           Not applicable.

SECTION 3. SECURITIES AND TRADING MARKETS

           Not applicable.

SECTION 4. MATTERS RELATED TO ACCOUNTANTS AND FINANCIAL STATEMENTS

           Not applicable.

SECTION 5. CORPORATE GOVERNANCE AND MANAGEMENT

           Not applicable.

SECTION 6. ASSET-BACKED SECURITIES

           Not applicable.

SECTION 7. REGULATION FD

           Not applicable.

<PAGE>


SECTION 8. OTHER EVENTS

              ITEM 8.01    OTHER EVENTS

                  99.1     Distribution to holders of the PreferredPLUS Trust
                           Certificates Series UPC-1 on December 15, 2005.

                                    For information with respect to the
                           underlying securities held by PreferredPLUS Trust
                           Series UPC-1, please refer to UnumProvident
                           Corporation's (Commission file number 001-11294)
                           periodic reports, including annual reports on Form
                           10-K, quarterly reports on Form 10-Q and current
                           reports on Form 8-K, and other information on file
                           with the Securities and Exchange Commission (the
                           "SEC"). You can read and copy these reports and other
                           information at the public reference facilities
                           maintained by the SEC at Room 1580, 100 F Street, NE,
                           Washington, D.C. 20549. You may obtain copies of this
                           material for a fee by writing to the SEC's Public
                           Reference Section of the SEC at 100 F Street, NE,
                           Washington, D.C. 20549. You may obtain information
                           about the operation of the Public Reference Room by
                           calling the SEC at 1-800-SEC-0330. You can also
                           access some of this information electronically by
                           means of the SEC's website on the Internet at
                           http://www.sec.gov, which contains reports, proxy and
                           information statements and other information that the
                           underlying securities issuer has filed electronically
                           with the SEC.

                                    Although we have no reason to believe the
                           information concerning the underlying securities or
                           the underlying securities issuer contained in the
                           underlying securities issuer's Exchange Act reports
                           is not reliable, neither the depositor nor the
                           trustee participated in the preparation of such
                           documents or made any due diligence inquiry with
                           respect to the information provided therein. No
                           investigation with respect to the underlying
                           securities issuer (including, without limitation, no
                           investigation as to its financial condition or
                           creditworthiness) or of the underlying securities has
                           been made. You should obtain and evaluate the same
                           information concerning the underlying securities
                           issuer as you would obtain and evaluate if you were
                           investing directly in the underlying securities or in
                           other securities issued by the underlying securities
                           issuer. There can be no assurance that events
                           affecting the underlying securities or the underlying
                           securities issuer have not occurred or have not yet
                           been publicly disclosed which would affect the
                           accuracy or completeness of the publicly available
                           documents described above.

<PAGE>


SECTION 9.        FINANCIAL STATEMENTS AND EXHIBITS

         ITEM 9.01    FINANCIAL STATEMENTS AND EXHIBITS


                  (a) Financial statements of business acquired.

                      Not Applicable.

                  (b) Pro forma financial information.

                      Not Applicable.

                  (c) Shell company transactions.

                      Not applicable.

                  (d) Exhibits.

                      99.1     Trustee's report in respect of the December
                               15, 2005 distribution to holders of the
                               PreferredPLUS Trust Certificates Series
                               UPC-1.



                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, hereunto duly authorized.


                                             MERRILL LYNCH DEPOSITOR, INC.

         Date: December 29, 2005             By: /s/ Zvi Gillon
                                                 ------------------------------
                                             Name:  Zvi Gillon
                                             Title: Vice President






<PAGE>






                                  EXHIBIT INDEX

99.1     Trustee's report in respect of the December 15, 2005 distribution to
         holders of the PreferredPLUS Trust Certificates Series UPC-1.
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SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549
                           --------------------------

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       The Securities Exchange Act of 1934
                            -------------------------

       Date of Report (Date of earliest event reported): December 15, 2005

                          MERRILL LYNCH DEPOSITOR, INC.
                 (ON BEHALF OF PREFERREDPLUS TRUST SERIES UPC-1)
             (Exact name of registrant as specified in its charter)

       DELAWARE                 001-31484                    13-3891329
   (State or other            (Commission                (I. R. S. Employer
   jurisdiction  of            File Number)              Identification No.)
    incorporation)

         WORLD FINANCIAL CENTER,                       10080
           NEW YORK, NEW YORK                       (Zip Code)
          (Address of principal
           executive offices)

                           --------------------------

       Registrant's telephone number, including area code: (212) 449-1000

                      INFORMATION TO BE INCLUDED IN REPORT

SECTION 1. REGISTRANT'S BUSINESS AND OPERATIONS

           Not applicable.

SECTION 2. FINANCIAL INFORMATION

           Not applicable.

SECTION 3. SECURITIES AND TRADING MARKETS

           Not applicable.

SECTION 4. MATTERS RELATED TO ACCOUNTANTS AND FINANCIAL STATEMENTS

           Not applicable.

SECTION 5. CORPORATE GOVERNANCE AND MANAGEMENT

           Not applicable.

SECTION 6. ASSET-BACKED SECURITIES

           Not applicable.

SECTION 7. REGULATION FD

           Not applicable.
SECTION 8. OTHER EVENTS

              ITEM 8.01    OTHER EVENTS

                  99.1     Distribution to holders of the PreferredPLUS Trust
                           Certificates Series UPC-1 on December 15, 2005.

                                    For information with respect to the
                           underlying securities held by PreferredPLUS Trust
                           Series UPC-1, please refer to UnumProvident
                           Corporation's (Commission file number 001-11294)
                           periodic reports, including annual reports on Form
                           10-K, quarterly reports on Form 10-Q and current
                           reports on Form 8-K, and other information on file
                           with the Securities and Exchange Commission (the
                           "SEC"). You can read and copy these reports and other
                           information at the public reference facilities
                           maintained by the SEC at Room 1580, 100 F Street, NE,
                           Washington, D.C. 20549. You may obtain copies of this
                           material for a fee by writing to the SEC's Public
                           Reference Section of the SEC at 100 F Street, NE,
                           Washington, D.C. 20549. You may obtain information
                           about the operation of the Public Reference Room by
                           calling the SEC at 1-800-SEC-0330. You can also
                           access some of this information electronically by
                           means of the SEC's website on the Internet at
                           http://www.sec.gov, which contains reports, proxy and
                           information statements and other information that the
                           underlying securities issuer has filed electronically
                           with the SEC.

                                    Although we have no reason to believe the
                           information concerning the underlying securities or
                           the underlying securities issuer contained in the
                           underlying securities issuer's Exchange Act reports
                           is not reliable, neither the depositor nor the
                           trustee participated in the preparation of such
                           documents or made any due diligence inquiry with
                           respect to the information provided therein. No
                           investigation with respect to the underlying
                           securities issuer (including, without limitation, no
                           investigation as to its financial condition or
                           creditworthiness) or of the underlying securities has
                           been made. You should obtain and evaluate the same
                           information concerning the underlying securities
                           issuer as you would obtain and evaluate if you were
                           investing directly in the underlying securities or in
                           other securities issued by the underlying securities
                           issuer. There can be no assurance that events
                           affecting the underlying securities or the underlying
                           securities issuer have not occurred or have not yet
                           been publicly disclosed which would affect the
                           accuracy or completeness of the publicly available
                           documents described above.
SECTION 9.        FINANCIAL STATEMENTS AND EXHIBITS

         ITEM 9.01    FINANCIAL STATEMENTS AND EXHIBITS

                  (a) Financial statements of business acquired.

                      Not Applicable.

                  (b) Pro forma financial information.

                      Not Applicable.

                  (c) Shell company transactions.

                      Not applicable.

                  (d) Exhibits.

                      99.1     Trustee's report in respect of the December
                               15, 2005 distribution to holders of the
                               PreferredPLUS Trust Certificates Series
                               UPC-1.

                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, hereunto duly authorized.

                                             MERRILL LYNCH DEPOSITOR, INC.

         Date: December 29, 2005             By: /s/ Zvi Gillon
                                                 ------------------------------
                                             Name:  Zvi Gillon
                                             Title: Vice President
EXHIBIT INDEX

99.1     Trustee's report in respect of the December 15, 2005 distribution to
         holders of the PreferredPLUS Trust Certificates Series UPC-1.