Abstract
BackgroundShort internodes contribute to plant dwarfism, which is exceedingly beneficial for crop production. However, the underlying mechanisms of internode elongation are complicated and have been not fully understood.ResultsHere, we report a maize dwarf mutant, dwarf2014 (d2014), which displays shortened lower internodes. Map-based cloning revealed that the d2014 gene is a novel br2 allele with a splicing variation, resulting in a higher expression of BR2-T02 instead of normal BR2-T01. Then, we found that the internode elongation in d2014/br2 exhibited a pattern of inhibition-normality-inhibition (transient for the ear-internode), correspondingly, at the 6-leaf, 12-leaf and 14-leaf stages. Indeed, BR2 encodes a P-glycoprotein1 (PGP1) protein that functions in auxin efflux, and our in situ hybridization assay showed that BR2 was mainly expressed in vascular bundles of the node and internode. Furthermore, significantly higher auxin concentration was detected in the stem apex of d2014 at the 6-leaf stage and strictly in the node region for the ear-internode at the 14-leaf stage. In such context, we propose that BR2/PGP1 transports auxin from node to internode through the vascular bundles, and excessive auxin accumulation in the node (immediately next to the intercalary meristem) region suppresses internode elongation of d2014.ConclusionsThese findings suggest that low auxin levels mediated by BR2/PGP1 in the intercalary meristem region are crucial for internode elongation.
Highlights
Short internodes contribute to plant dwarfism, which is exceedingly beneficial for crop production
Unlike GAs and BRs, the reduction in plant height of SL mutants may be an indirect effect of increased tillers because the deficiency in SLs enhances cell division in axillary meristems (AMs) [19, 20], which leads to a redirection of the nutrition toward tiller growth instead of internode elongation
We explored the specific location of BR2 expression in the stem and detected the dynamic variation of auxin concentration so as to reveal the mechanism of internode elongation by BR2/PGP1-mediated auxin transport
Summary
Short internodes contribute to plant dwarfism, which is exceedingly beneficial for crop production. There are several GA-related mutants that display extremely reduced height with uniformed short internodes, such as dwarf1(d1), d3, d5 and anther ear (an1), as well as dominant mutants D8 and D9 [11,12,13], all of which influence internode elongation throughout the growth period, accompanied by a certain degree of yield loss. Unlike GAs and BRs, the reduction in plant height of SL mutants may be an indirect effect of increased tillers because the deficiency in SLs enhances cell division in axillary meristems (AMs) [19, 20], which leads to a redirection of the nutrition toward tiller growth instead of internode elongation
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