Abstract
The appropriate timing of the termination of floral meristem activity (FM determinacy) determines the number of floral organs. In Arabidopsis, two transcription factors, CRABS CRAW (CRC) and SUPERMAN (SUP), play key roles in FM determinacy. CRC belongs to the YABBY transcription factor family, whose members contain a zinc finger and a helix-loop-helix domain. The crc mutation causes the formation of unfused carpels and leads to an increase in carpel number in sensitized backgrounds. The SUP gene encodes a C2H2-type zinc-finger protein, and sup mutants produce extra carpels and stamens. However, the genetic interaction between CRC and SUP is not fully understood. Here, we show that these two transcription factors regulate multiple common downstream genes during stamen development. The crc sup double mutant had significantly more stamens and carpels than the parental lines and an enlarged floral meristem. Transcriptome data have implicated several cytokinin- and auxin-related genes as well as stress- and metabolic-related genes to function downstream of CRC and SUP during stamen development. The regulation of common downstream genes of CRC and SUP might contribute to the initiation of an appropriate number of stamens and to subsequent growth and development.
Highlights
Plant development is dependent on the persistent activity of pluripotent meristematic cells that are responsible for organ formation (Laux et al, 1996)
We previously identified two CRABS CRAW (CRC) direct and auxin-related targets, which are responsible for floral meristem (FM) termination (Yamaguchi et al, 2017, 2018): TORNADO2 (TRN2) encodes a transmembrane protein of the tetraspanin family and controls auxin homeostasis (Cnops et al, 2006; Chiu et al, 2007) and YUCCA4 (YUC4) is one of the 11 YUCCA genes that encode flavin monooxygenases involved in tryptophan-dependent auxin biosynthesis (Cheng et al, 2006, 2007)
It is generally reported that auxin and cytokinin function antagonistically, recent studies have revealed that they act synergistically during gynoecium formation (Wolters and Jurgens, 2009; El-Showk et al, 2013; Schaller et al, 2015; Müller et al, 2017; Reyes-Olalde et al, 2017a,b). These findings have demonstrated that the interplay between auxin and cytokinin via ARABIDOPISIS HISTIDINE PHOSPHOTRANSFER PROTEIN6 (AHP6) is important for floral primordium positioning and gynoecium formation, the role of AHP6 in FM determinacy and floral organ initiation remains unclear
Summary
Plant development is dependent on the persistent activity of pluripotent meristematic cells that are responsible for organ formation (Laux et al, 1996). In Arabidopsis, the FM is maintained by activity of the WUSCHEL (WUS) homeodomain protein and CLAVATA (CLV) ligand–receptor system (Laux et al, 1996; Brand et al, 2000; Schoof et al, 2000). The WUS–CLV negative feedback loop controls the balance between stem-cell renewal and organ formation and determines the size and number of floral organs, which are sepals, petals, stamens, and carpels (Schoof et al, 2000; Sun et al, 2009). Lossof-function mutants of any of the CLV genes results in enlarged FMs and leads to an increase in floral organ number (Clark et al, 1993, 1995; Kayes and Clark, 1998). The WUS–CLV negative feedback loop is essential to control FM activity
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