Tryptophan-dependent auxin biosynthesis is required for HD-ZIP III-mediated xylem patterning

Abstract

The development and growth of higher plants is highly dependent on the conduction of water and minerals throughout the plant by xylem vessels. In Arabidopsis roots the xylem is organized as an axis of cell files with two distinct cell fates: the central metaxylem and the peripheral protoxylem. During vascular development, high and low expression levels of the class III HD-ZIP transcription factors promote metaxylem and protoxylem identities, respectively. Protoxylem specification is determined by both mobile, ground tissue-emanating miRNA165/6 species, which downregulate, and auxin concentrated by polar transport, which promotes HD-ZIP III expression. However, the factors promoting high HD-ZIP III expression for metaxylem identity have remained elusive. We show here that auxin biosynthesis promotes HD-ZIP III expression and metaxylem specification. Several auxin biosynthesis genes are expressed in the outer layers surrounding the vascular tissue in Arabidopsis root and downregulation of HD-ZIP III expression accompanied by specific defects in metaxylem development is seen in auxin biosynthesis mutants, such as trp2-12, wei8 tar2 or a quintuple yucca mutant, and in plants treated with L-kynurenine, a pharmacological inhibitor of auxin biosynthesis. Some of the patterning defects can be suppressed by synthetically elevated HD-ZIP III expression. Taken together, our results indicate that polar auxin transport, which was earlier shown to be required for protoxylem formation, is not sufficient to establish a proper xylem axis but that root-based auxin biosynthesis is additionally required.

Cytokinin-Auxin Crosstalk in the Gynoecial Primordium Ensures Correct Domain Patterning

“…This is in line with observations made from various auxin biosynthetic components in other tissues (Stepanova et al, 2008;Ursache et al, 2014), where researchers have postulated that the discrepancy between auxin biosynthesis and signaling peaks likely underscores the necessity of a functional auxin transport system to correctly position auxin maxima for various developmental processes.…”

MultiSite Gateway-Compatible Cell Type-Specific Gene-Inducible System for Plants

“…L4, Gateway recombination site attL4; R1, attR1; L1, attL1; L2, attL2; R2, attR2; L3, attL3; B4, attB4; B1, attB1; B2, attB2; B3, attB3; XVE, chimeric transcription factor containing the DNAbinding domain of LexA, the transcriptional activation domain of VP16, and the regulatory domain of the human estrogen receptor; e9T, rbcS E9 poly(A) addition sequence; nosT, nopaline synthase poly(A) addition sequence; pLexA, eight copies of the LexA operator sequence together with a minimal cauliflower mosaic virus 35S promoter. Odell et al, 1985) Yes (data not shown) p1R4-p6xUAS:XVE Upstream activation sequence containing several GAL4-binding elements and minimal 35S (Brand and Perrimon, 1993;Johnson et al, 2005) Yes (Vatén et al, 2011) p1R4-pAHP6:XVE Protoxylem + protoxylem-pericycle, organ primordia in shoot apical meristem/ARABIDOPSIS HISTIDINE PHOSPHOTRANSFER PROTEIN6 (AHP6)/AT1G8010 (Mähö nen et al, 2006;Bartrina et al, 2011;Besnard et al, 2014) Yes (Mähö nen et al, 2014) p1R4-pANT:XVE Developing ovules, primordia of all lateral shoot organs/ AINTEGUMENTA/AT4G37750 (Elliott et al, 1996) Yes (data not shown) p1R4-pAPL:XVE Phloem (developing sieve elements and companion cells)/ALTERED PHLOEM DEVELOPMENT (APL)/AT1G79430 (Bonke et al, 2003) Yes (Bishopp et al, 2011b;Vatén et al, 2011) p1R4-pAtSUC2:XVE Phloem companion cells/ARABIDOPSIS THALIANA SUCROSE-PROTON SYMPORTER2/AT1G22710 (Truernit and Sauer, 1995) Yes (data not shown) p1R4-pCALS3:XVE Vascular bundle, root stem cell niche/CALLOSE SYNTHASE3 (CALS3)/ AT5G13000 (Vatén et al, 2011) Yes (Vatén et al, 2011) p1R4-pCCS52A1:XVE Root elongation zone, lateral roots/CELL CYCLE SWITCH PROTEIN52 A1 (CCS52A1)/AT4G22910 (Vanstraelen et al, 2009) Yes (data not shown) p1R4-pCO2:XVE Cortex/CORTEX2 (CO2)/AT1G62500 (Heidstra et al, 2004) Yes (Dhonukshe et al, 2010; this article) p1R4-pCYP79B3:XVE Meristem quiescent center and the surrounding stem cells/ CYTOCHROME P450, FAMILY 79, SUBFAMILY B3 (CYP79B3)/ AT2G22330 (Ljung et al, 2005) Yes (data not shown) p1R4-pG1090:XVE Strong ubiquitous expression/G10-90 (artificial promoter containing repeats of G-box; Ishige et al, 1999) Yes ( Yes (Bishopp et al, 2011a;Vatén et al, 2011;Ursache et al, 2014; this article) p1R4-pWOX5:XVE Root meristem quiescent ce...…”

Transcriptome atlas of the Arabidopsis funiculus – a study of maternal seed subregions

“…We therefore suggest that the analysis of ARFs and Aux/IAAs expressed specifically in the funiculus could provide insight into how auxin response in the funiculus affects seed development. Auxin has been shown to be necessary for vascular development in Arabidopsis (Cheng et al, 2006;Ursache et al, 2014). During ovule development, auxin response in the funiculus is localized to the developing vascular tissue (Pagnussat et al, 2009).…”