Wh. Cheng et al., THE MINIATURE1 SEED LOCUS OF MAIZE ENCODES A CELL-WALL INVERTASE REQUIRED FOR NORMAL DEVELOPMENT OF ENDOSPERM AND MATERNAL CELLS IN THE PEDICEL, The Plant cell, 8(6), 1996, pp. 971-983
Collective evidence demonstrates that the Miniature1 (Mn1) seed locus
in maize encodes an endosperm-specific isozyme of cell wall invertase,
CWI-2. The evidence includes (1) isolation and characterization of et
hyl methanesulfonate-induced mn1 mutants with altered enzyme activity
and (2) a near-linear relationship between geneldose and invertase act
ivity and the CWI-2 protein. In addition, molecular analyses showed th
at the cBNA clone incw2 maps to the Mn1 locus and differentiates the s
ix ethyl methanesulfonate-induced mn1 mutants of independent origin in
to two classes when RNA gel blot analyses were used. We also report tw
o unexpected observations that provide significant new insight into th
e physiological role of invertase and its regulation in a developing s
eed. First, a large proportion of total enzyme activity (similar to 90
%) was dispensable (i.e., nonlimiting). However, below the threshold l
evel of similar to 6% of wild-type activity, the endosperm enzyme cont
rolled both the sink strength of the developing endosperm as well as t
he developmental stability of maternal cells in the pedicel in a rate-
limiting manner. Our data also suggest an unusually tight coordinate c
ontrol between the cell wall-bound and the soluble forms of invertase,
which are most likely encoded by two separate genes, presumably throu
gh metabolic controls mediated by the sugars.