SUGAR AND METABOLIC-REGULATION OF GENES FOR SUCROSE METABOLISM - POTENTIAL INFLUENCE OF MAIZE SUCROSE SYNTHASE AND SOLUBLE INVERTASE RESPONSES ON CARBON PARTITIONING AND SUGAR SENSING

Sugar responsiveness of genes for both paths of sucrose metabolism cou ld provide a mechanism not only for transcriptional regulation of the first step in the use of imported carbon, but also for altering signal s to the sugar-sensing system. This hypothesis was examined by compari son of (1) sugar regulation among maize genes for sucrose synthase and invertase, (2) their contrasting patterns of tissue expression, and ( 3) their influence on production of effecters for other sugar-responsi ve genes. Cloning and characterization of the lvr1 and lvr2 invertase genes of maize indicated that these genes belong to distinct subfamili es of the maize soluble invertase gene family. In addition, maize inve rtases can be grouped with the sucrose synthases (Sh1 and Sus1) on the basis of shared patterns of differential sugar-responsiveness and tis sue-specific expression. Extension of this comparison to include genes for sucrose metabolism from other species revealed a more widespread association between starvation-tolerant expression and restricted patt erns of tissue distribution. Consideration of current models for plant sugar-sensing systems and transport pathways suggested that the site and mechanism of sucrose cleavage in the cell could affect the magnitu de and type of signal generated.