Histidine limitation causes alteration in the TOR network and plant development

Plant growth depends on growth regulators, nutrient availability, and amino acids levels. The TOR (Target of Rapamycin) network senses these parameters and influences cell wall formation and expansion accordingly. Cell wall integrity and structures are surveyed and modified by a complex array of cell wall integrity sensors, including LRR-extensins (LRXs), that function as hormone receptors and help to compact cell walls. Expressing the Arabidopsis root-hair specific LRX1 without the extensin domain, which anchors the protein to the cell wall, has a negative effect on root hair development. The mechanism of this negative effect was investigated by a suppressor screen, which led to the identification of a sune ( suppressor of dominant-negative LRX1 ) mutant collection. The sune82 mutant was identified as an allele of HISN2 which encodes an enzyme essential for histidine biosynthesis. The sune82 mutation leads to reduced accumulation of histidine, and this influences the TOR network. The sune82 mutant reflects the impact of the TOR network on cell wall formation processes involving LRX proteins. It also represents an excellent tool to study the effects of reduced histidine levels on plant development, as it is a rare example of a viable partial loss-of-function allele in an essential biosynthetic pathway.