Genetic Control of Anther Cell Division and Differentiation 373
direct localization to the nucleus (Ito and Shinozaki 2002). Thus, MS1 appears
to be a nuclear protein involved in regulating transcription either through al-
tering chromatin structure or as a transcription factor (Aasland et al. 1995; Ito
and Shinozaki 2002; Wilson et al. 2001).
6
Summary and Perspectives
Many exciting discoveries have been made in the realm of anther devel-
opment within the last ten years. The early actingSPL/NZZgene is a key
regulator of sporogenous cell differentiation and encodes a putative tran-
scription factor. Its function is likely coordinated with other factors important
for differentiation of the early anther cell types. Between stages 2 and 5, cells
within the anther lobes undergo highly oriented cell divisions and the fac-
tors governing this process are not yet known. Further studies in the near
future will likely uncover additional genes that control anther differentiation,
including genes that are regulated by SPL/NZZ.
EMS/EXS,SERK1,SERK2,andTPD1appear to function in the same sig-
naling pathway to promote tapetum differentiation. It is possible that the
proteins coded for by these genes physically interact. EMS/EXS may form
a functional receptor complex with SERK1 and/or SERK2, and TPD1 may be
the ligand for this complex. In addition, other LRR-RLKs may also play a role
in other aspects of anther development. The currently ongoing 2010 project
on the functional analysis of 30 LRR-RLKs (http://www.mcb.arizona.edu/tax/
2010/index.htm) may yield further insight into the regulation of anther devel-
opment by members of this important gene family.
Finally, several genes have been described that are important for both
tapetum and pollen development. Interestingly,Udt1appears to regulate the
expression of a potential rice homolog forAMS(Os02g02820). Thus, theAra-
bidopsishomolog ofUdt1may regulate the expression ofAMS. If this is the
case, it would indicate that this transcriptional pathway for tapetum devel-
opment and/or function is highly conserved between monocots and dicots.
Tapetum and pollen development are complex and important processes, fu-
ture studies using multiple approaches offer the promise of new discoveries
about the molecular control of plant development.
AcknowledgementsWe greatly appreciate the contributions of figures by Drs. Takuya Ito,
Anthony Millar, and William Sheridan. We would also like to thank Bridget Leyland and
Gavilange Nestor for comments on the manuscript. The work in our laboratory has been
supported by a grant from the US Department of Energy to H.M. (DE-FG02-02ER15332).
C.L.H.H. was partially supported by the Integrative Bioscience Graduate Degree Program
at the Pennsylvania State University.