From spatio-temporal morphogenetic gradients to rhythmic patterning at the shoot apex

Abstract

A key question in developmental biology is how morphogenetic regulators control patterning.Recent findings have raised an important question: do morphogenetic signals carry information not only in space, as originally proposed in the morphogen concept, but also in time? The hormone auxin is an essential plant morphogenetic regulator that drives rhythmic organogenesis at the shoot apical meristem. Here, we used a quantitative imaging approach to map auxin distribution and response. We demonstrate the existence of high-definition spatiotemporal auxin distribution in the meristem. We provide evidence that developing organs are auxin-emitting centers that could allow self-sustained distribution of auxin through a structured auxin transport network converging on the meristem center. We finally

The Diverse Roles of Auxin in Regulating Leaf Development

“…The central high-auxin zone forms periodical protrusions that coincide with incipient primordia, which is specified by the duration of cell exposure to auxin. The duration of auxin exposition may explain the robust and rhythmical phyllotactic patterning [20]. Further, and contrary to many prior published results, auxin flow in incipient and newly-formed primordia largely points toward the SAM, thus creating the previously observed high auxin zone.…”

“…However, this viewpoint has been challenged by recent studies involving high-resolution imaging of the localization of PIN1 and the auxin biosensor DII-Venus. According to these studies, the central zone of the SAM generally contains high levels of auxin, although low levels of auxin signaling occur in this region [19,20]. The central high-auxin zone forms periodical protrusions that coincide with incipient primordia, which is specified by the duration of cell exposure to auxin.…”

In Arabidopsis, low blue light enhances phototropism by releasing cryptochrome 1-mediated inhibition ofPIF4expression

“…Consistent with these findings, the pin3pin4pin7 triple mutant was unable to bend in all tested conditions (Figure 7A). The analysis of an epidermis specific variant of the ratiometric auxin reporter qDII-Venus (Galvan-Ampudia et al, 2019) one hour after phototropic stimulation revealed the presence of an auxin gradient across the hypocotyl both in SUN/LBL and LBL/LBL (Figure 7B). Interestingly, in persistent LBL condition, the gradient was steeper correlating with the faster phototropic response (Figures 2, 7B).…”

“…pPIF4:PIF4-HApif4-101cry1-304, pPIF4:PIF4-HApif4-101cry1-304cry2-1, cry1-304phot1-5 were obtained by crosses and the primers used for genotyping are listed in Supplemental Table1. The epidermis specific promoter PDF1 (protodermal factor 1) (Abe et al, 2001) driving the expression of a DII-VENUS-N7-2A-TagBFP-sv40 (qDII) (Galvan-Ampudia et al, 2019) was assembled by Gateway technology (Invitrogen) and transformed in Arabidopsis thaliana (Col-0).…”

WUSCHEL acts as a rheostat on the auxin pathway to maintain apical stem cells inArabidopsis

“…Given the dynamic and self-organizing nature of the auxin system in the SAM 38 , the independent spatial input provided by WUS appears to be required to bar differentiation competence from the center of the SAM, while at the same time still allowing to sense this important signal. In light of the findings that PIN1 mediated auxin flux in the SAM may be directed towards the center 39 , it is tempting to speculate that auxin could serve as a positional signal not only for organ initiation, but also for stem cells. Genotyping revealed that all arrested plants were homozygous for wus-7.…”