SUGAR REGULATION OF HARVEST-RELATED GENES IN ASPARAGUS

The signals controlling the abundance of transcripts up-regulated (pTI P27, pTIP31, and pTIP32) or down-regulated (pTIP20 and pTIP21) after h arvest in asparagus (Asparagus officinalis L.) spears were examined. p TIP27 and pTIP31 are known to encode asparagine synthetase (AS) and a beta-galactosidase (beta-gal) homolog, respectively. The nucleotide se quences of pTIP20, pTIP21, and pTIP32 were determined, and they encode histone 3, histone 2B, and an unknown product, respectively. Changes in respiration, soluble sugars, and abundance of the five mRNAs were s imilar in the tips stored as 30-mm lengths or as part of 180-mm spears . We previously hypothesized that sugars may regulate the level of AS transcripts in asparagus tissue. Asparagus cell cultures were used to test the role of sugar status in regulating gene expression. Transcrip t abundance for AS, beta-gal, and pTIP32 was low in cells in sugar-con taining medium but increased within 12 h after transferring cells to a sugar-free medium. Histone 3 and histone 2B transcripts were, in gene ral, abundant in cells on sugar-containing medium but declined in abun dance when transferred to sugar-free medium. When cells were returned to sugar-containing medium the abundance of transcripts for histone 3 and histone 2B increased, whereas that for AS, beta-gal, and pTIP32 de creased. Soluble sugar levels are known to decline rapidly in the tips of harvested spears. Metabolic regulation by sugar status may have a major influence on gene expression in asparagus spears and other tissu es after harvest.