Lysigenous aerenchyma formation: responsiveness to waterlogging in oil palm roots

Oil palm (Elaeis guineensis Jacq.) responds to waterlogging stress by induction of lysigenous aerenchyma tissues, which facilitates the flow of oxygen through their root tissues for survival under waterlogged conditions. Thus, the morphological and genetic adaptation involved in lysigenous aerenchyma formation in the roots of the oil palm genotype Deli × Calabar under waterlogging stress was evaluated. This study found the highest number of dead cells after waterlogging stress for 2 d in the secondary root, while the percentage of root porosity was increased with increasing of time in both roots, especially at 1.0 - 2.0 cm from the root tip. This change in cell morphology implied the formation of lysigenous aerenchyma in oil palm roots under waterlogging stress. At the same time, most of the candidate genes involved in lysigenous aerenchyma formation revealed a higher mRNA expression after waterlogging stress for 3 d. Genes of ethylene synthesis group ACS3, ACO, and ACO1 were highly up-regulated in both types of roots, while XTH22, XTH23, and CEL12 in the cell wall modification group were more highly up-regulated in the primary roots than in the secondary roots. CML11, CAMTA4, TCTP, and CPI1 in a signaling group were up-regulated in the primary roots, but they were down-regulated in the secondary roots. NAC29, ERF1, ERF113, and HSFA2C in a transcription factor group were strongly up-regulated in the oil palm roots. However, there have been no previous reports on the expression of CAMTA4, bHLH79, and bHLH94 under waterlogging conditions. Our findings confirm gene expression during lysigenous aerenchyma development in oil palm roots under waterlogging. It can also be stated that primary roots are an important part of the adaptation mechanism of oil palm roots for survival under waterlogging stress. Furthermore, the molecular markers of all expressed genes will be developed and applied in our oil palm breeding project for selection of waterlogging tolerance.