AnAGAMOUS-Related MADS-Box Gene,XAL1(AGL12), Regulates Root Meristem Cell Proliferation and Flowering Transition in Arabidopsis    

Abstract

MADS-box genes are key components of the networks that control the transition to flowering and flower development, but their role in vegetative development is poorly understood. This article shows that the sister gene of the AGAMOUS (AG) clade, AGL12, has an important role in root development as well as in flowering transition. We isolated three mutant alleles for AGL12, which is renamed here as XAANTAL1 (XAL1): Two alleles, xal1-1 and xal1-2, are in Columbia ecotype and xal1-3 is in Landsberg erecta ecotype. All alleles have a short-root phenotype with a smaller meristem, lower rate of cell production, and abnormal root apical meristem organization. Interestingly, we also encountered a significantly longer cell cycle in the strongest xal1 alleles with respect to wild-type plants. Expression analyses confirmed the presence of XAL1 transcripts in roots, particularly in the phloem. Moreover, XAL1Tb-glucuronidase expression was specifically up-regulated by auxins in this tissue. In addition, mRNA in situ hybridization showed that XAL1 transcripts were also found in leaves and floral meristems of wildtype plants. This expression correlates with the late-flowering phenotypes of the xal1 mutants grown under long days. Transcript expression analysis suggests that XAL1 is an upstream regulator of SOC, FLOWERING LOCUS T, and LFY. We propose that XAL1 may have similar roles in both root and aerial meristems that could explain the xal1 late-flowering phenotype.

The genome sequence of the orchid Phalaenopsis equestris

“…However, genes in both the AGL12 and AGL15 clades are present in the genomes of rice and A. thaliana; therefore, orthologs of FLC, AGL12 and AGL15 might have been specifically lost in orchids. Although AGL12-like genes (XAL1 in A. thaliana) are necessary for root development and flowering 46 , it seems that a different mechanism has evolved in P. equestris for the same function. Genes in the B-class AP3, C/D-class and E-class clades are well known for their roles in the specification of floral organ identity and have been well studied in P. equestris.…”

Longitudinal zonation pattern inArabidopsisroot tip defined by a multiple structural change algorithm

“…This result suggests that XAL1 is involved in the regulation of the transition from the PD to the TD. Interestingly, the L critD is altered by the loss of function of XAL1, suggesting that the longer cell cycle duration estimated in xal1 roots (Tapia-Lopez et al, 2008) is possibly related to alterations in the size-sensing mechanisms that control the onset of cell division. Fully elongated cells of xal1 roots are shorter on average than wt ones (Tapia-Lopez et al, 2008).…”

“…Root thickness was measured at the level corresponding to the PD/TD boundary for cortex determined by experienced biologists, which implies a subjective method, abbreviated here as the ExpBiol method. The PD/TD boundary determined by an ExpBiol method was defined for epidermis and cortex, arbitrarily based on relative changes in cell lengths or internuclear distances along the root, similar to other studies (Rost and Baum, 1988;Dubrovsky, 1997;Dubrovsky et al, 1998a, b;Tapia-Lopez et al, 2008;Garay-Arroyo et al, 2013).…”

“…XAANTAL1 (XAL1) or AGL12 is a member of the MADS box family of genes, which encode transcription factors important for regulating plant and animal development. This gene participates in the regulation of cell proliferation in the arabidopsis RAM (Tapia-Lopez et al, 2008). Loss-of-function allelic mutants have shorter roots and lower root growth rates than wild type (wt), explained by a shorter RAM, lower rates of cell production and a longer cell cycle duration than wt roots (Tapia-Lopez et al, 2008).…”

“…This gene participates in the regulation of cell proliferation in the arabidopsis RAM (Tapia-Lopez et al, 2008). Loss-of-function allelic mutants have shorter roots and lower root growth rates than wild type (wt), explained by a shorter RAM, lower rates of cell production and a longer cell cycle duration than wt roots (Tapia-Lopez et al, 2008). We used the proposed MSC approach to analyse arabidopsis wt and loss-of-function xal1-2 (hereafter xal1) mutant roots.…”