In search of the still unknown function of FW2.2/CELL NUMBER REGULATOR, a major regulator of fruit size in tomato

Abstract

The FW2.2 gene is associated with the major Quantitative Trait Locus (QTL) governing fruit size in tomato, and acts by negatively controlling cell division during fruit development. FW2.2 belongs to a multigene family named the CELL NUMBER REGULATOR (CNR) family. The CNR proteins harbour the uncharacterized PLAC8 motif made of two conserved cysteine-rich domains separated by a variable region that are predicted to be transmembrane segments, and indeed FW2.2 localizes to the plasma membrane. Although FW2.2 was cloned more than two decades ago, the molecular mechanisms of FW2.2 action remain unknown. Especially, how FW2.2 functions to regulate cell cycle and fruit growth, and thus fruit size, is yet not understood. We here review the current knowledge on PLAC8-containing CNR/FWL proteins in plants, which are described to participate in plant organogenesis and the regulation of organ size, especially in fruits, and in Cadmium resistance, ion homeostasis and/or Ca2+ signalling. Within the plasma membrane, FW2.2 and some CNR/FWL are localized in microdomains, which is supported by recent data from interactomics studies. Hence FW2.2 and CNR/FWL could be involved in a transport function of signalling molecules across membranes, thus influencing organ growth via a cell-to-cell trafficking mechanism.

Liguleless narrow and narrow odd dwarf act in overlapping pathways to regulate maize development and metabolism

“…Moreover, a recent study found that some polymorphisms in NOD alleles among maize genotypes are significantly associated with yield‐related traits in ear morphology (Zuo et al., 2021 ). Thus, NOD and NOD‐like proteins play crucial roles in agricultural species, and they could even be useful targets for plant breeders (Beauchet et al., 2021 ). Mechanistically, the Arabidopsis orthologs of NOD were first identified for their ability to complement loss of a Ca 2+ channel in yeast (and thus named MID1‐COMPLEMENTING ACTIVITY or MCA), hinting that NOD could act as a plasma membrane Ca 2+ channel (Nakagawa et al., 2007 ), although there have been conflicting reports using different methodologies to test whether NOD is capable of trafficking ions across plasma membranes in heterologous Xenopus oocyte systems (Furuichi et al., 2012 ; Rosa et al., 2017 ).…”

Mutation in OsFWL7 Affects Cadmium and Micronutrient Metal Accumulation in Rice

“…Numerous studies have suggested that plasma membrane-associated plant FWL proteins perform diverse functions, such as cell division and organ development control, and heavy metal uptake and translocation [24,25]. However, the mechanisms underlying their distinct roles remain elusive.…”

“…The FW2.2 protein harbors an uncharacterized placenta-specific 8 domain, and is localized to the plasma membrane [21,22]. FW2.2-like (FWL) genes have been characterized in various plant species and reported to perform diverse functions [23][24][25]. Cell Number Regulator1 (CNR1), an FWL gene in maize, negatively regulates plant and organ size by controlling cell division [22].…”

Just enough fruit: understanding feedback mechanisms during sexual reproductive development

“…Numerous genes and QTLs are involved in tomato yield and individual fruit weight (reviewed in Ariizumi et al , 2013 ). For instance, Fruit Weight 2.2 (FW2.2) is a transcription factor that inhibits cell division ( Beauchet et al , 2021 ). Due to sequence variation in its promoter region, it is expressed at higher levels in wild tomatoes than in cultivated lines, causing a small fruit phenotype.…”