Expression Profiling of Sugar-Starch Pathway Genes in Waxy Maize with Contrasting Sucrose Content

초록

Waxy maize (Zea mays L.) is valued for its amylopectin-rich sticky texture, but kernels typically accumulate low levels of soluble sugars compared with sweet corn. To identify gene-expression features associated with naturally higher sweetness in waxy backgrounds, we quantified soluble sugars in developing kernels and profiled transcription of key sucrose-starch pathway genes. Soluble sugars (sucrose, glucose, and fructose) were quantified by high-performance liquid chromatography (HPLC) from kernels harvested 21 days after pollination (DAP) from 58 waxy inbred lines classified into kernel-color groups (BS, CS, YS, RS, and S), with sweet-corn cultivars included as high-sugar references. Within waxy groups, YS and RS consistently showed higher mean sucrose than BS lines across years, while RS also maintained relatively higher glucose and fructose. For expression analysis, 20 contrasting genotypes (two low- and two high-sucrose lines per group) were selected and transcript abundance of 25 pathway genes was measured by quantitative real-time PCR (qRT-PCR) in endosperm and embryo tissues. Most genes showed higher transcript abundance in endosperm than embryo. Among functional gene categories, starch branching enzyme genes exhibited the clearest association with sucrose differences: endosperm expression of starch branching enzyme I (SBEI) increased in high-sucrose cultivars across both years, whereas SBEIIa (amylose extender1) and SBEIIb displayed group-dependent and often complementary patterns. These results highlight natural variation in downstream starch-assembly genes as a plausible lever to fine-tune sugar retention in waxy kernels, providing candidate targets and germplasm resources for breeding moderately sweeter waxy maize without the severe starch penalties of classical sweet-corn mutants.

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