A SIMILAR DICHOTOMY OF SUGAR MODULATION AND DEVELOPMENTAL EXPRESSION AFFECTS BOTH PATHS OF SUCROSE METABOLISM - EVIDENCE FROM A MAIZE INVERTASE GENE FAMILY
J. Xu et al., A SIMILAR DICHOTOMY OF SUGAR MODULATION AND DEVELOPMENTAL EXPRESSION AFFECTS BOTH PATHS OF SUCROSE METABOLISM - EVIDENCE FROM A MAIZE INVERTASE GENE FAMILY, The Plant cell, 8(7), 1996, pp. 1209-1220
Invertase and sucrose synthase catalyze the two known paths for the fi
rst step in carbon use by sucrose-importing plant cells. The hypothesi
s that sugar-modulated expression of these genes could provide a means
of import adjustment was initially suggested based on data from sucro
se synthases alone; however, this hypothesis remained largely conjectu
ral without critical evidence for invertases. Toward this end, a famil
y of maize invertases was cloned and characterized. Here, we show that
invertases are indeed sugar modulated and, surprisingly, like the suc
rose synthase genes, fall into two classes with contrasting sugar resp
onses, In both families, one class of genes is upregulated by increasi
ng carbohydrate supply (Sucrose synthase1 [Sus1] and Invertase2 [Ivr2]
), whereas a second class in the same family is repressed by sugars an
d upregulated by depletion of this resource (Shrunken1 [Sh1] and Inver
tase1 [Ivr1]), The two classes also display differential expression du
ring development, with sugar-enhanced genes (Sus1 and Ivr2) expressed
in many importing organs and sugar-repressed, starvation-tolerant gene
s (Sh1 and Ivr1) upregulated primarily during reproductive development
. Both the Ivr1 and Ivr2 invertase mRNAs ate abundant in root tips, ve
ry young kernels, silk, anthers, and pollen, where a close relationshi
p is evident between changes in message abundance and soluble invertas
e activity. During development, patterns of expression shift as assimi
late partitioning changes from elongating silks to newly fertilized ke
rnels, Together, the data support a model for integrating expression o
f genes differentially responsive to carbohydrate availability (i.e.,
feast and famine conditions) with developmental signals, The demonstra
tion that similar regulatory patterns occur in both paths of sucrose m
etabolism indicates a potential to influence profoundly the adjustment
of carbon resource allocation.