Cell-to-Cell Movement of Two Interacting AT-Hook Factors inArabidopsisRoot Vascular Tissue Patterning

Abstract

The xylem and phloem, major conducting and supporting tissues in vascular plants, are established by cell division and celltype specification in the procambium/cambium. The organization of the xylem, phloem, and procambium/cambium is tightly controlled. However, the underlying regulatory mechanisms remain largely unknown. In this study, we report the discovery of two transcription factors, AT-HOOK MOTIF NUCLEAR LOCALIZED PROTEIN 3 (AHL3) and AHL4, which regulate vascular tissue boundaries in Arabidopsis thaliana roots. In either of the knockout mutants of AHL3 and AHL4, encoding closely related AT-hook transcription factors, a misspecification of tissue boundaries between the xylem and procambium occurred and ectopic xylem developed in the procambium domain. In plants, specific types of transcription factors can serve as direct intercellular signals by moving from one cell to another, playing crucial roles in tissue patterning. Adding to this paradigm, AHL4 moves actively from the procambium to xylem in the root meristem to regulate the tissue boundaries. When the intercellular movement of AHL4 was impaired, AHL4 could not complement the xylem phenotype in the ahl4. Furthermore, AHL4 revealed unique characteristics in that it interacts with AHL3 in vivo and that this interaction facilitates their intercellular trafficking. Taken together, this study uncovered a novel mechanism in vascular tissue patterning that requires the intercellular trafficking of two interacting transcription factors.

Arabidopsis thaliana AHL family modulates hypocotyl growth redundantly by interacting with each other via the PPC/DUF296 domain

“…development, including hypocotyl elongation in the light (AHL22, ESC/AHL27, and SOB3/AHL29) (16,17), flower development (16)(17)(18)(19)(20), and root growth (21). Overexpression of other AHL gene members, such as HERCULES (HRC/AHL25), also enhances adult leaf and stem growth (22).…”

Vascular Cambium Development

“…7). Furthermore, an LRR-RLK transcript coexpressed with PXY, PXY/TDR-CORRELATED GENES1 (PXC1; At2g36570), is required for xylem fiber formation in stem secondary vasculature (Wang et al, 2013). Another RLK, XYLEM INTERMIXED WITH PHLOEM/C-TERMINALLY ENCODED PEPTIDE RECEPTOR 1 (XIP1/CEPR1; At5g49660) prevents the ectopic lignification of phloem in stems (Bryan et al, 2012).…”

“…Loss of all five HD-ZIP III genes results in a complete lack of xylem accompanied by an increased number of procambial cell files, while low levels of HD-ZIP III expression induce protoxylem, and overexpression leads to metaxylem formation (Carlsbecker et al, 2010). AT-HOOK MO-TIF NUCLEAR LOCALIZED PROTEIN3 (AHL3; At4g25320) and AHL4 (At5g51590), which also move to the xylem axis from the surrounding tissues, regulate the boundary between xylem and procambium (Zhou et al, 2013). Altogether, the morphogenesis of the root vascular bundle is seen to be regulated by antagonistic networks of laterally moving intercellular signals, including auxin, cytokinins, mobile transcription factors, and microRNAs.…”

Transcriptome dynamics of developing maize leaves and genomewide prediction ofciselements and their cognate transcription factors

“…Many of them are implicated in development, such as LATERAL ORGAN BOUNDARIES (LBD) (T018-T048) in organ boundary determination (57), SBP (T030-T066) in vegetative phase change, branching, and leaf initiation rate (58), HMGI/HMGY (T030-T096, T132) in vascular tissue patterning (26), YABBY (T054-T072) in the regulation of abaxialadaxial polarity (59), TEOSINTE BRANCHED1, CYCLOIDEA and PROLIFERATING CELL FACTORS (TCP) (T030-T132) in cell proliferation (60), and THREE-AMINO ACID-LOOP-EXTENSION (TALE) (T036-T048 and T096-T192) in meristem formation or maintenance and secondary cell wall biosynthesis (61,62). The most highly expressed TALE gene is orthologous to KNOTTED-LIKE FROM ARABIDOPSIS3 (KNAT3), which is light-and cytokinin-regulated and which modulates ABA response during germination and early seedling development (61,63).…”