A FLOODING-INDUCED XYLOGLUCAN ENDO-TRANSGLYCOSYLASE HOMOLOG IN MAIZE IS RESPONSIVE TO ETHYLENE AND ASSOCIATED WITH AERENCHYMA

Development of aerenchyma (soft cortical tissue with large intercellul ar air spaces) in flooded plants results from cell-wall hydrolysis and eventual cell lysis and is promoted by endogenous ethylene. Despite i ts adaptive significance, the molecular mechanisms behind aerenchyma d evelopment remain unknown. We recently isolated a flooding-induced mai ze (Zea mays L.) gene (wusl1005[gfu]; abbreviated as 1005) encoding a homolog of xyloglucan endo-transglycosylase (XET), a putative cell-wal l-loosening enzyme active during germination, expansion, and fruit sof tening. XET and related enzymes may also be involved in cell-wall meta bolism during flooding-induced aerenchyma development. Under flooding, 1005 mRNA accumulated in root and mesocotyl locations that subsequent ly exhibited aerenchyma development and reached maximum levels within 12 h of treatment. Aerenchyma development was observed in the same loc ations by 48 h of treatment. Treatment with the ethylene synthesis inh ibitor (aminooxy)acetic acid (AOA), which prevented cortical air space formation under flooding, almost completely inhibited 1005 mRNA accum ulation in both organs. AOA treatment had little effect on the accumul ation of mRNA encoded by adh1, indicating that it did not cause genera l suppression of flooding-responsive genes. Additionally, ethylene tre atment under aerobic conditions resulted in aerenchyma development as well as induction of 1005 in both organs. These results indicate that 1005 is responsive to ethylene. Treatment with anoxia, which suppresse s ethylene accumulation and aerenchyma development, also resulted in 1 005 induction. However, in contrast to flooding, AOA treatment under a noxia did not affect 1005 mRNA accumulation, indicating that 1005 is i nduced via different mechanisms under flooding (hypoxia) and anoxia.