Functional Analysis Of Maize Seed Imbibition Protein Gene ZmAGA4

Alkaline Alpha Galactosidase/AGA is a seed imbibition protein/SIP that hydrolyzes raffinose.We have cloned four AGA/SIP genes from maize genome and named these genes as ZmAGA1 to ZmAGA4.These ZmAGAs shared high homology,and grouped to the AGA gene family.The ZmAGA4 gene is induced by high temperature.Further investigation led to the identification of a heat shock element in the promoter of ZmAGA4.ZmAGA4 was transformed into Arabidopsis thaliana and two transgenic lines were obtained.The two ZmAGA4 expressing Arabidopsis lines show higher survival rate than control groups after heat shock stress.The ZmAGA4 lines accumulate less reactive oxygen species than the control lines.These data demonstrate that ZmAGA4 plays an important role in high temperature stress tolerance.The raffinose and galactinol content decreased in ZmAGA4 expressing lines,suggesting that ZmAGA4 might be involved in the raffinose metabolism pathway.ZmAGA4 expressing Arabidopsis plants show accelerated growth,shorter life cycle.There is an unknown sugar in ZmAGA4 expressing Arabidopsis seeds and the seeds are more sensitive to aging.We postulate that ZmAGA4 might be involved in sugar metabolism and generate more glucose to accelerate the metabolism of the cell,thus enhanced the respiratoryrate.The relevant proteins in the seed might be degraded faster in ZmAGA4 expressing seeds,thus,the seeds are more vulnerble to aging.