Arabidopsis guard cell chloroplasts import cytosolic ATP for starch turnover and stomatal opening

Abstract

Stomatal opening requires the provision of energy in the form of ATP for proton pumping across the guard cell (GC) plasma membrane and for associated metabolic rearrangements. The source of ATP for GCs is a matter of ongoing debate that is mainly fuelled by controversies around the ability of GC chloroplasts (GCCs) to perform photosynthesis. By imaging compartment-specific fluorescent ATP and NADPH sensor proteins in Arabidopsis, we show that GC photosynthesis is limited and mitochondria are the main source of ATP. Unlike mature mesophyll cell (MC) chloroplasts, which are impermeable to cytosolic ATP, GCCs import cytosolic ATP through NUCLEOTIDE TRANSPORTER (NTT) proteins. GCs from ntt mutants exhibit impaired abilities for starch biosynthesis and stomatal opening. Our work shows that GCs obtain ATP and carbohydrates via different routes from MCs, likely to compensate for the lower chlorophyll contents and limited photosynthesis of GCCs.

The green light gap: a window of opportunity for optogenetic control of stomatal movement

“…However, recent data obtained using a genetically encoded ATP sensor showed that guard cell chloroplasts of Arabidopsis have only a very limited ATP production capacity. In fact, these chloroplasts take up ATP from the cytosol in the light to support starch synthesis (Lim et al ., 2022). It is thus likely that PAR provokes stomatal opening via another signal, such as the intracellular ATP level in guard cells.…”

Leaf starch metabolism sets the phase of stomatal rhythm

“…Beyond this speculation around sugar-phosphates, the activity of MEX1 may carry a lot of weight in the homeostasis of the guard cell metabolism, either through a direct subcellular compartmentation of some sugars or phosphate intermediates, or through an indirect feedback of maltose transport on the metabolic network. The fluxes of metabolites and ions between the different compartments of the cell are highly interlocked and critically important for CO 2 -and light-induced stomatal movements (Shimazaki et al, 1989(Shimazaki et al, , 2007Robaina-Estévez et al, 2017;Jezek et al, 2021;Lim et al, 2022), that were markedly disturbed in mex1. The mex1 mutation may disturb this delicate metabolic equilibrium between organelles that normally enables proper stomatal behaviour -and starch synthesis in the guard cells.…”

Bioenergetics of pollen tube growth in Arabidopsis thaliana revealed by ratiometric genetically encoded biosensors

“…Here, to delineate the above processes, we introduced in planta ATP 26 , NADPH, and NADH/NAD + ratiometric biosensors 27 , 28 into Arabidopsis pollen. Since the first-generation NADPH and NADH/NAD + ratiometric biosensors are pH-sensitive, an independent transgenic line expressing a control biosensor is needed for post-experimental pH normalization 27 , 28 .…”

“…Here, to delineate the above processes, we introduced in planta ATP 26 , NADPH, and NADH/NAD + ratiometric biosensors 27 , 28 into Arabidopsis pollen. Since the first-generation NADPH and NADH/NAD + ratiometric biosensors are pH-sensitive, an independent transgenic line expressing a control biosensor is needed for post-experimental pH normalization 27 , 28 . To visualize dynamic changes of NADPH levels and NADH/NAD + ratio in individual pollen plastids or in the cytosol without pH normalization, we developed pH insensitive (pH 7.0 to 8.5) versions of these pyridine nucleotide biosensors by fusing a mCherry fluorophore at the N termini of the iNAPs and SoNar, as a mCherry-iNap1 fusion protein has been reported previously 29 .…”