Environmental and developmental regulation of the wound-induced cell wall protein WI12 in the halophyte ice plant

A wounded gene WI12 was used as a marker to examine the interaction between biotic stress (wounding) and abiotic stress (high salt) in the facultative halophyte ice plant (Mesembryanthemum crystallinum). The deduced WI12 amin o acid sequence has 68% similarity to WUN1, a known potato (Solanum tuberos um) wound-induced protein. Wounding, methyl jasmonate, and pathogen infecti on induced local WI12 expression. Upon wounding, the expression of WI12 rea ched a maximum level after 3 h in 4-week-old juvenile leaves, whereas the m aximum expression was after 24 h in 8-week-old adult leaves. The temporal e xpression of WI12 in salt-stressed juvenile leaves was similar to that of a dult leaves. The result suggests that a salt-induced switch from C3 to Cras sulacean acid metabolism has a great influence on the ice plant's response to wounding. The expression of WI12 and the accumulation of WI12 protein we re constitutively found in phloem and in wounded mesophyll cells. At the re productive stage, WI12 was constitutively found in petals and styles, and d evelopmentally regulated in the placenta and developing seeds. The histoche mical analysis showed that the appearance of WI12 is controlled by both env ironmental and developmental factors. Immunogold labeling showed WI12 prefe rentially accumulates in the cell wall, suggesting its role in the reinforc ement of cell wall composition after wounding and during plant development.