<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): August 15, 2006

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

          DELAWARE             001-16835                    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


Check the appropriate box below if the Form 8-K filing is intended to
simultaneously satisfy the filing obligation of the registrant under any of the
following provisions (see General Instruction A.2.):

[ ]  Written communications pursuant to Rule 425 under the Securities Act (17
     CFR 230.425)

[ ]  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR
     240.14a-12)

[ ]  Pre-commencement communications pursuant to Rule 14d-2(b) under the
     Exchange Act (17 CFR 240.14d-2(b))

[ ]  Pre-commencement communications pursuant to Rule 13e-4(c) under the
     Exchange Act (17 CFR 240.13e-4(c))


<PAGE>

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 ALL-1 on August 15, 2006.

                           For information with respect to the underlying
                  securities held by PreferredPLUS Trust Series ALL-1, please
                  refer to The Hanover Insurance Group Inc.'s (Commission file
                  number 001-13754) 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 guarantor and the underlying securities
                  issuer has filed electronically with the SEC.


<PAGE>

                           Although we have no reason to believe the information
                  concerning the underlying securities, the junior subordinated
                  debentures and the underlying guarantee or the underlying
                  securities issuer and the underlying securities guarantor
                  contained in the underlying securities guarantor'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 or the underlying securities
                  guarantor (including, without limitation, no investigation as
                  to their respective financial condition or creditworthiness)
                  or of the underlying securities, the junior subordinated
                  debentures or the underlying guarantee has been made. You
                  should obtain and evaluate the same information concerning the
                  underlying securities issuer and the underlying securities
                  guarantor 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 or the
                  underlying securities guarantor. There can be no assurance
                  that events affecting the underlying securities, the junior
                  subordinated debentures and the underlying guarantee or the
                  underlying securities issuer and the underlying securities
                  guarantor 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 August 15, 2006
                           distribution to holders of the PreferredPLUS Trust
                           Certificates Series ALL-1.

<PAGE>

                                   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: 08/25/2006                     By: /s/ Jason Liddell
                                         ------------------------------
                                     Name: Jason Liddell
                                     Title: Vice-President


<PAGE>


                                  EXHIBIT INDEX


99.1     Trustee's report in respect of the August 15, 2006 distribution to
         holders of the PreferredPLUS Trust Certificates Series ALL-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): August 15, 2006

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

          DELAWARE             001-16835                    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

Check the appropriate box below if the Form 8-K filing is intended to
simultaneously satisfy the filing obligation of the registrant under any of the
following provisions (see General Instruction A.2.):

[ ]  Written communications pursuant to Rule 425 under the Securities Act (17
     CFR 230.425)

[ ]  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR
     240.14a-12)

[ ]  Pre-commencement communications pursuant to Rule 14d-2(b) under the
     Exchange Act (17 CFR 240.14d-2(b))

[ ]  Pre-commencement communications pursuant to Rule 13e-4(c) under the
     Exchange Act (17 CFR 240.13e-4(c))
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 ALL-1 on August 15, 2006.

                           For information with respect to the underlying
                  securities held by PreferredPLUS Trust Series ALL-1, please
                  refer to The Hanover Insurance Group Inc.'s (Commission file
                  number 001-13754) 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 guarantor and the underlying securities
                  issuer has filed electronically with the SEC.
Although we have no reason to believe the information
                  concerning the underlying securities, the junior subordinated
                  debentures and the underlying guarantee or the underlying
                  securities issuer and the underlying securities guarantor
                  contained in the underlying securities guarantor'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 or the underlying securities
                  guarantor (including, without limitation, no investigation as
                  to their respective financial condition or creditworthiness)
                  or of the underlying securities, the junior subordinated
                  debentures or the underlying guarantee has been made. You
                  should obtain and evaluate the same information concerning the
                  underlying securities issuer and the underlying securities
                  guarantor 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 or the
                  underlying securities guarantor. There can be no assurance
                  that events affecting the underlying securities, the junior
                  subordinated debentures and the underlying guarantee or the
                  underlying securities issuer and the underlying securities
                  guarantor 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 August 15, 2006
                           distribution to holders of the PreferredPLUS Trust
                           Certificates Series ALL-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: 08/25/2006                     By: /s/ Jason Liddell
                                         ------------------------------
                                     Name: Jason Liddell
                                     Title: Vice-President
EXHIBIT INDEX

99.1     Trustee's report in respect of the August 15, 2006 distribution to
         holders of the PreferredPLUS Trust Certificates Series ALL-1.