<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): September 15, 2005

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

        DELAWARE                     001-16507                  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.
<PAGE>

SECTION 6.        [RESERVED]

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 ATT-1 on September 15, 2005.

                                   For information with respect to the
                  underlying securities held by PreferredPLUS Trust Series
                  ATT-1, please refer to AT&T Corp.'s (Commission file number
                  001-01105) 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) Exhibits.

                           99.1     Trustee's report in respect of the September
                                    15, 2005 distribution to holders of the
                                    PreferredPLUS Trust Certificates Series
                                    ATT-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: September 23, 2005        By:      /s/ Stephan Kuppenheimer
                                                  ---------------------------
                                         Name:    Stephan Kuppenheimer
                                         Title:   President




                                  EXHIBIT INDEX


                  99.1     Trustee's report in respect of the September 15, 2005
                           distribution to holders of the PreferredPLUS Trust
                           Certificates Series ATT-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): September 15, 2005

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

        DELAWARE                     001-16507                  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.        [RESERVED]

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 ATT-1 on September 15, 2005.

                                   For information with respect to the
                  underlying securities held by PreferredPLUS Trust Series
                  ATT-1, please refer to AT&T Corp.'s (Commission file number
                  001-01105) 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) Exhibits.

                           99.1     Trustee's report in respect of the September
                                    15, 2005 distribution to holders of the
                                    PreferredPLUS Trust Certificates Series
                                    ATT-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: September 23, 2005        By:      /s/ Stephan Kuppenheimer
                                                  ---------------------------
                                         Name:    Stephan Kuppenheimer
                                         Title:   President

                                  EXHIBIT INDEX

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