Interfering with leucine biosynthesis affects the TOR network and causes changes in cell growth that lead to suppression of the cell wall formation mutant
lrx1
.
Lead (Pb) is an important pollutant
of worldwide concern with respect
to extensive pollution sources and highly toxic effect. Flavonol can
improve plant resistance to abiotic stress and is also responsible
for the alleviating effect under Pb stress. The relationship between
Pb stress and flavonol and the knowledge about the mechanisms of flavonol
function are very limited. Pb affected the energy metabolism process
and, thus, inhibited plant growth and development. Flavonol accumulation
controlled by FLS1 (flavonol synthase) could alleviate the toxic effect.
Importantly, nes (mutant of NES that allows FLS1 to enter the nucleus
expression) showed better growth status and lighter oxidative damage
than NES (N-terminal nucleus exclusion signal peptide prevents FLS1
from entering the nucleus expression), which indicated that nucleus
flavonol synthesized by nucleus FLS1 plays a key
role in plant resistance to Pb stress. Although FLS1 signals were detected in the cell membrane, cytoplasm, and nucleus,
membrane flavonol, cytoplasm flavonol, and nucleus flavonol were not
exercising their function in the corresponding position. The expression
of nucleus FLS1 intervened in the total content and
composition of flavonol. The results also revealed that nucleus flavonol
could regulate the ascorbate metabolism for alleviating the damage
on the chloroplast, thus maintaining the photophosphorylation pathway.
Our findings provided new insights for the molecular basis of Pb tolerance
and response mechanism of the plant.
Plant cell growth involves coordination of numerous processes and signaling cascades among the different cellular compartments to concomitantly enlarge the protoplast and the surrounding cell wall. In Arabidopsis thaliana, the cell wall integrity-sensing process involves the extracellular LRX (LRR-Extensin) proteins that bind RALF (Rapid ALkalinization Factor) peptide hormones and, in vegetative tissues, interact with the transmembrane receptor kinase FERONIA (FER). This LRX/RALF/FER signaling module influences cell wall composition and regulates cell growth. The numerous proteins involved in or influenced by this module are beginning to be characterized. In a genetic screen, mutations in Apyrase 7 (APY7) were identified to suppress growth defects observed in lrx1 and fer mutants. APY7 encodes a Golgi-localized NTP-diphosphohydrolase, but opposed to other apyrases of Arabidopsis, APY7 revealed to be a negative regulator of cell growth. APY7 modulates the growth-inhibiting effect of RALF1, influences the cell wall architecture, and alters the pH of the extracellular matrix, all of which affect cell growth. Together, this study reveals a function of APY7 in cell wall formation and cell growth that is connected to growth processes influenced by the LRX/FER/RALF signaling module.
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