| Summary: | 博士 === 國立臺灣大學 === 植物學研究所 === 91 === A 7-kDa-proteinase inhibitor, designated SPLTI (Sweet Potato Leaf Trypsin Inhibitor) was partially purified from sweet potato (Ipomoea batatas Lam.) leaves under water deficit condition. The N-terminal amino acid sequence was determined and used to design two overlap degenerate primers for isolation of the SPLTI gene. Two full-length cDNA clones encoding proteinase inhibitor I (PI-I), designated SPLTI-a and SPLTI-b, were isolated. Both SPLTI-a and SPLTI-b are 98 % identical to each other in both levels of nucleotide and amino acid sequence. Southern blot analysis showed that SPLTI was encoded by a small gene family. Using SPLTI-a as a probe, we found that SPLTI gene exhibited a leaf-specific expression patterns. Additionally, this was the first report that the SPLTI genes were up-regulated by water deficiency and chilling as well as osmoticant treatments in the PI-I family in plants. As other proteinase inhibitors, the SPLTI transcripts were induced by wounding and also by exogenous applications of abscisic acid (ABA) and methyl jasmonate (MeJA); however, accumulation of the wound-induced transcripts were restricted locally in the injured leaves, but not systemically. Transient expression assay of GUS-SPLTI fusion protein in onion epidermal cells, using particle bombardment techniques, suggested that SPLTI may localize in cytoplasma. The distinct expression patterns of SPLTI provided a new insight to the regulation of PI-I gene family in response to environmental stresses. Our results suggested that SPLTI may play a role against environmental stresses through regulation of endogenous proteolytic activities during leaf development.
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