Lecureuil, A. | Search bioRxiv

bioRxiv2024

Innovative mutant screening identifies TRANSPARENT TESTA7 as a player in seed oil/protein partitioning

Brassicaceae species mainly accumulate oil and protein in their seeds, which are essential to human life as a source of food, but also as animal feed and resources for green chemistry. To date, Brassicaceae crops such as rapeseed have been selected mainly for their oil content. However, there is a growing interest in their seed protein content. A strong negative correlation between oil and protein content makes it difficult to increase both compounds simultaneously. In this study, an Arabidopsis thaliana homozygous EMS mutant library was screened by near-infrared spectroscopy for seed oil and protein content, with the aim of identifying mutants with impaired oil-protein correlation. The mutant most affected in this correlation was found to be in the TRANSPARENT TESTA7 gene, which is involved in the flavonoid biosynthetic pathway. Analysis of different mutants in the flavonoid pathway revealed that the tt7 mutants were the only ones to show such a significant reduction in seed oil content, highlighting a phenotype never described before for the tt7 mutants and suggesting a specific role for TT7 in the interplay between the oil and flavonoid biosynthetic pathways. Untargeted metabolomic analysis allowed the identification of metabolic features that are highly accumulated and specific to tt7 seeds compared to the other genotypes and genetic analysis established that the accumulation of kaempferol-3-O-rhamnoside seems to be responsible for the seed oil reduction of tt7 mutants. Significance StatementBrassicaceae species accumulate oil and protein in their seeds and understanding how the partitioning of these compounds is regulated is necessary to engineer seeds for specific purposes. By screening an Arabidopsis EMS mutant library, we identified mutants affected in seed oil/protein partitioning, including tt7, highlighting a link between oil and flavonoid biosynthetic pathways, that we explore further in this paper.

plant biology↗

bioRxiv2023

Physcomitrium patens SMXL homologs are PpMAX2-dependent negative regulators of growth

SMXL proteins are a plant-specific clade of type I HSP100/Clp-ATPases. SMXL genes are found in virtually all land plant genomes. However, they have mainly been studied in angiosperms. In Arabidopsis thaliana, three SMXL functional subclades have been identified: SMAX1/SMXL2, SMXL345 and SMXL678. Out of these, two subclades ensure transduction of endogenous hormone signals: SMAX1/SMXL2 are involved in KAI2-ligand (KL) signaling, while SMXL678 are involved in strigolactone (SL) signaling. Many questions remain regarding the mode of action of these proteins, as well as their ancestral role. We addressed these questions by investigating the function of the four SMXL genes of the moss Physcomitrium patens. We demonstrate that PpSMXL proteins are involved in the conserved ancestral MAX2-dependent KL signaling pathway and act as negative regulators of growth. However, PpSMXL proteins expressed in A. thaliana unexpectedly cannot replace SMAX1/SMXL2 function in KL signaling, whereas they can functionally replace SMXL4/5 and restore root growth. Therefore, the molecular function of SMXL could be conserved, but not their interaction network. Moreover, one PpSMXL clade positively regulates transduction of the SL signal in P. patens. So far, this function has only been reported herein in moss, where it represents a novel crosstalk between SL and KL signaling pathways.

plant biology↗