Scarecrow gene, promoter and uses thereof

Details Scarecrow gene, promoter and uses thereof Scarecrow gene, promoter and uses thereof

1999-03-10

2004-10-26

Fox, David T. (Department: 1638)

Multicellular living organisms and unmodified parts thereof and

Method of introducing a polynucleotide molecule into or...

The polynucleotide alters plant part growth

C800S287000, C800S278000, C536S023600, C435S419000, C435S320100, C435S468000

Reexamination Certificate

active

06809234

ABSTRACT:

1. INTRODUCTION
The present invention generally relates to the SCARECROW (SCR) gene family and their promoters. The invention more particularly relates to ectopic expression of members of the SCARECROW gene family in transgenic plants to artificially modify plant structures. The invention also relates to utilization of the SCARECROW promoter for tissue and organ specific expression of heterologous gene products.
2. BACKGROUND OF THE INVENTION
Asymmetric cell divisions, in which a cell divides to give two daughters with different fates, play an important role in the development of all multicellular organisms. In plants, because there is no cell migration, the regulation of asymmetric cell divisions is of heightened importance in determining organ morphology. In contrast to animal embryogenesis, most plant organs are not formed during embryogenesis. Rather, cells that form the apical meristems are set aside at the shoot and root poles. These reservoirs of stem cells are considered to be the source of all post-embryonic organ development in plants. A fundamental question in developmental biology is how meristems function to generate plant organs.
2.1. Root Development
Root organization is established during embryogenesis. This organization is propagated during postembryonic development by the root meristem. Following germination, the development of the postembryonic root is a continuous process, wherein a series of initials or stem cells continuously divide to perpetuate the pattern established in the embryonic root (Steeves & Sussex, 1972
, Patterns in Plant Development
, Englewood Cliffs, N.J.: Prentice-Hall, Inc.).
2.1.1. Arabidopsis Root Development
Due to the organization of the Arabidopsis root, it is possible to follow the fate of cells from the meristem to maturity and identify the progenitors of each cell type (Dolan et al., 1993, Development 119:71-84). The Arabidopsis root is a relatively simple and well characterized organ. The radial organization of the mature tissues in the Arabidopsis root has been likened to tree rings with the epidermis, cortex, endodermis and pericycle forming radially symmetric cell layers that surround the vascular cylinder (FIG.
1
A). See also Dolan et al., 1993, Development 119:71-84. These mature tissues are derived from four sets of stem cells or initials: i) the columella root cap initial; ii) the pericycle/vascular initial; iii) the epidermal/lateral root cap initial; and iv) the cortex/endodermal initial (Dolan et al., 1993, Development 119:71-84). It has been'shown that these initials undergo asymmetric divisions (Scheres et al., 1995, Development 121:53-62). The cortex/endodermal initial, for example, first divides anticlinally (in a transverse orientation) (FIG.
1
B). This asymmetric division produces another initial and a daughter cell. The daughter cell, in turn, expands and then divides periclinally (in the longitudinal orientation) (FIG.
1
B). This second asymmetric division produces the progenitors of the endodermis and the cortex cell lineages (FIG.
1
B).
Furthermore, root radial organization in Arabidopsis is produced by three distinct developmental strategies. First, primary roots employ stem cells, wherein initials undergo asymmetric divisions first to regenerate themselves and then to generate the cell lineages of the root (FIG.
1
B). Second, in the embryo, sequential asymmetric divisions subdivide pre-existing tissue to form the cell layers of the embryonic root. Finally, lateral roots are formed by a strategy of cell proliferation that originates in differentiated tissues. Remarkably, within a given species, all three strategies result in roots with a nearly identical radial organization.
2.1.2. Maize Root Development
The root organization of
Zea mays
(maize), which is a very well characterized member of the grass family, is far more complex than the root organization in Arabidopsis. The root system of maize consists of primary, embryonic, lateral, seminal lateral and adventitious roots. Both primary and seminal lateral roots are formed during embryogenesis, wherein the primary root is the first root to emerge during germination, followed by the seminal lateral roots formed at the scutellar nodal region (Freeling, M. and Walbot, V. (1994), The Maize Handbook, (New York: Springer-Verlag); Hetz, W. et al., (1996), Plant J. 10:845-857). Both crown and prop roots which develop post-embryonically are shoot-borne roots, often termed “adventitious”. However, since these roots are part of the normal development of the plant, they are not, strictly speaking, adventitious roots, which are typically formed as a result of injury or hormone treatment. Crown roots, representing the major roots of the mature plant, are formed at consecutive early nodes of the stem beginning with the coleoptilar nodes. Later in development, brace or prop roots emerge from nodes above the soil level (Freeling, M. and Walbot, V. (1994), The Maize Handbook, (New York: Springer-Verlag); Hetz, W. et al., (1996), Plant J. 10:845-857).
Currently, there are two notably different types of organization of root apical meristems: an open and a closed meristem. In an “open” meristem, the cell files of the mature tissues cannot be traced with much confidence to distinct initials, and the incipient tissues do not appear to have discrete boundary walls between the root proper and the root cap (Clowes, F. A. L., 1981, Ann. Bot. 48:761-767). Therefore, the interpretation of the organization of the open meristem has been problematic (Clowes, F. A. L., 1981, Ann. Bot. 48:761-767). In a “closed” meristem, however, since files of cells converge onto a pole at the root apex, it is easy to identify discrete layers in median longitudinal sections (Clowes, F. A. L., 1981, Ann. Bot. 48:761-767).
Both Arabidopsis and maize roots show characteristics of the closed meristem (FIGS.
23
A-B). However, there are important differences. In maize roots, the root apical meristem consists of three independent layers of initials. One gives rise to the stele, the second gives rise to epidermis, cortex and endodermis and the third generates the root cap, whereas in the Arabidopsis root apical meristem, the epidermis shares a common initial with the lateral root cap (Esau, K., 1977, Anatomy of Seed Plants. 2nd ed. (New York: John Wiley & Sons); Esau, K., 1953, Plant Anatomy. (New York: John Wiley & Sons)).
Primary organization of the root apical meristem in maize occurs during embryogenesis, (Steeves, T. A. and Sussex, I. M., (1989), Patterns in plant development., 2nd ed. (Cambridge University Press)) as in Arabidopsis. There are three main phases in embryo development in maize (
FIGS. 24A-B
) (Freeling, M. and Walbot, V. (1994), The Maize Handbook, (New York: Springer-Verlag); Steeves, T. A. and Sussex, I. M. (1989), Patterns in plant development., 2nd ed., (Cambridge University Press); Sheridan, W. F. and Clark, J. K., (1993), Plant J. 3:347-358). As in Arabidops is, the very first division of the zygote establishes the initial asymmetry of the embryo (FIG.
24
A). However, unlike Arabidopsis, embryonic development in maize is characterized by rather irregular cell divisions (Sheridan, W. F. and Clark, J. K., (1993), Plant J. 3:347-358). During the first phase, the apical-basal asymmetry of the embryo is established, and the embryo is regionalized into suspensor and embryo proper (FIGS.
24
B-C). During the second phase, radial asymmetry appears and the embryonic axis and meristems are established (
FIGS. 24D-E
) (Clowes, F. A. L., (1978), New Phytol. 80:409-419). Finally, during the third phase, vegetative structures such as embryonic roots and leaves are elaborated (
FIGS. 24F-G
) (Sheridan, W. F. and Clark, J. K., (1993), Plant J. 3:347-358).
2.1.3. The Quiescent Center
The quiescent center (QC) of root apical meristems of angiosperms is a population of mitotically inactive cells. In the QC of the primary root of maize, for example, the average duration of a mitotic cycle is about 200 hours compared with only 12 hours in the cells just below the QC and 28 hours in the cells ju

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