Dynamic Regulation of Auxin Response during Rice Development Revealed by Newly Established Hormone Biosensor Markers

Abstract

The hormone auxin is critical for many plant developmental processes. Unlike the model eudicot plant Arabidopsis (Arabidopsis thaliana), auxin distribution and signaling in rice tissues has not been systematically investigated due to the absence of suitable auxin response reporters. In this study we observed the conservation of auxin signaling components between Arabidopsis and model monocot crop rice (Oryza sativa), and generated complementary types of auxin biosensor constructs, one derived from the Aux/IAA-based biosensor DII-VENUS but constitutively driven by maize ubiquitin-1 promoter, and the other termed DR5-VENUS in which a synthetic auxin-responsive promoter (DR5rev) was used to drive expression of the yellow fluorescent protein (YFP). Using the obtained transgenic lines, we observed that during the vegetative development, accumulation of DR5-VENUS signal was at young and mature leaves, tiller buds and stem base. Notably, abundant DR5-VENUS signals were observed in the cytoplasm of cortex cells surrounding lateral root primordia (LRP) in rice. In addition, auxin maxima and dynamic re-localization were seen at the initiation sites of inflorescence and spikelet primordia including branch meristems (BMs), female and male organs. The comparison of these observations among Arabidopsis, rice and maize suggests the unique role of auxin in regulating rice lateral root emergence and reproduction. Moreover, protein localization of auxin transporters PIN1 homologs and GFP tagged OsAUX1 overlapped with DR5-VENUS during spikelet development, helping validate these auxin response reporters are reliable markers in rice. This work firstly reveals the direct correspondence between auxin distribution and rice reproductive and root development at tissue and cellular level, and provides high-resolution auxin tools to probe fundamental developmental processes in rice and to establish links between auxin, development and agronomical traits like yield or root architecture.

Translating auxin responses into ovules, seeds and yield: Insight from Arabidopsis and the cereals

“…In maize and rice, auxin activity is detected during early endosperm development, using the DR5 auxin reporter (Chen et al ; Yang et al ), which correlates with accumulation of IAA in the endosperm (Chourey et al ; Abu‐Zaitoon et al ). After fertilization in maize, PIN1 is up‐regulated in the endosperm and localizes to the plasma membrane during cellularization (Forestan et al ).…”

Fluorescent reporter lines for auxin and cytokinin signalling in barley (Hordeum vulgare)

“…With this study, we started to address the roles of auxin and cytokinin in barley root and shoot meristem development at cellular resolution. We found that the DR5 and DR5v2 regulatory elements that are successfully used in many other plant species to determine auxin signalling were not consistently expressed in our transgenic barley lines (Liao et al, 2015;Yang et al, 2017;Forestan et al, 2012) (Supplementary figure 5). In Arabidopsis, the two auxin reporters DR5 and DR5v2 showed differences in their expression patterns, indicating that ARFs have different binding affinity towards the respective auxin response elements TGTCTC (DR5) and TGTCGG (DR5v2) (Liao et al, 2015).…”

“…In Arabidopsis, the responsiveness of these reporters to auxin was confirmed by auxin application to the roots, leading to an enhanced expression of the reporter gene and a broadening of the expression domain (Liao et al, 2015). The same reporters were successfully used in rice and maize to display the spatial domain of auxin signalling (Yang et al, 2017;Gallavotti et al, 2008), therefore, the same regulatory sequences might be usable to monitor auxin signalling in barley. Surprisingly, no expression of the DR5:GFP reporter could be detected in transgenic lines with this construct, and expression of the DR5v2:VENUS-H2B reporter lines was very weak and inconsistent between different roots and plant lines (Supplementary figure 5A, B).…”

“…In the Arabidopsis shoot apical meristem (SAM), these reporters uncovered auxin maxima in the primordia, and high levels of cytokinins in the center of the meristem and the primordia. In the root apical meristems (RAM), an auxin maximum is formed in the Quiescent Center (QC), in the columella initials and in differentiated columella cells, while cytokinin maxima are observed in the differentiated columella and the stele (Aida et al, 2004;Sabatini et al, 1999;Yang et al, 2017;Benková et al, 2003;Zurcher et al, 2013). Post-embryonic development of plant organs depends on the activity of meristems, and this specific phytohormone distribution was shown to be required for meristem patterning (Sabatini et al, 1999;Blilou et al, 2005;Reinhardt et al, 2003;Stahl and Simon, 2005).…”

Genome-Wide Identification of GH3 Genes in Brassica Oleracea and Identification of a Promoter Region for Anther-Specific Expression of a GH3 Gene

“…We suspect that deletion of promoter sequences (-278 ~ -155) close to the transcription start site makes anther-speci c expression depend on the genomic positions where transgene is inserted. In Arabidopsis, Male Sterility 1 plant homeodomain-nger and MYB99 transcription factors functioning in anther and pollen development pathway are expressed in microspores, polarized microspores, and bicellular pollens [49,57]. The ndings (1) that Bo2g011210 is strongly expressed when microspores, polarized microspores, and bicellular pollens are produced and (2) that MYB core cis-acting element (CTGTTA) is located at -293 ~ -288 raises a possibility that TO1000 ortholog of Arabidopsis MYB99 play an important role for anther-speci c expression of Bo2g011210 [58].…”