Auxin is required for the long coleoptile trait in japonica rice under submergence

Abstract

Rice coleoptile elongation under submergence guarantees fast seedling establishment in the field. We investigated the role of auxin in influencing the capacity of rice to produce a long coleoptile under water. In order to explore the complexity of auxin's role in coleoptile elongation, we used gene expression analysis, confocal microscopy of an auxin-responsive fluorescent reporter, gas chromatography coupled to tandem mass spectrometry (GC-MS/MS), and T-DNA insertional mutants of an auxin transport protein. We show that a higher auxin availability in the coleoptile correlates with the final coleoptile length under submergence. We also identified the auxin influx carrier AUX1 as a component influencing this trait under submergence. The coleoptile tip is involved in the final length of rice varieties harbouring a long coleoptile. Our experimental results indicate that auxin biosynthesis and transport underlies the differential elongation between short and long coleoptile-harbouring japonica rice varieties.

Molecular Mechanisms Supporting Rice Germination and Coleoptile Elongation under Low Oxygen

“…Some authors hypothesised that the rice endosperm releases auxin during low O 2 . Rice grain contains IAA [ 19 ], which may be translocated to the elongating coleoptile. A key role in auxin transport has been proved by the phenotype of osaux1 mutants, which shows a reduced coleoptile length under submergence in comparison to the background [ 19 ].…”

“…Rice grain contains IAA [ 19 ], which may be translocated to the elongating coleoptile. A key role in auxin transport has been proved by the phenotype of osaux1 mutants, which shows a reduced coleoptile length under submergence in comparison to the background [ 19 ]. This result is very interesting also in relation to the possible auxin interaction with ethylene, as previously suggested, and the positive effect of ethylene on coleoptile growth.…”

“…Under submergence, the rice coleoptile can grow several days without apparent senescence; it then reaches a plateau where cell extension is likely at a maximum [ 19 , 20 ]. At this plateau stage, different rice varieties show variability in coleoptile length, which can be a trait of genetic origin ( Figure 1 ).…”

“…EXPA7 expression was found to be positively regulated by target-mimic lines of miR393, and negatively by miR393 overexpressing lines. Subsequently, EXPA7 expression has been found to be significantly regulated in japonica rice varieties that have a long coleoptile [ 19 ]. A role for auxin availability and transport mediated by AUX1 has been identified in long coleoptile harbouring varieties [ 19 ].…”

“…Subsequently, EXPA7 expression has been found to be significantly regulated in japonica rice varieties that have a long coleoptile [ 19 ]. A role for auxin availability and transport mediated by AUX1 has been identified in long coleoptile harbouring varieties [ 19 ]. In these varieties, the coleoptile tip likely induces a further production or redistribution of auxin along the coleoptile longitudinal axis that culminates in an increased length.…”