The Stomatal Openings Occurred from Blue Light Photoreceptors Mediated Signal Transduction Pathway May be Enhanced by a Blue Light Stimulated Photosynthesis

Sensory control of sporulation in Physarum polycephalum plasmodia is mediated by a branched signal-transduction pathway that integrates blue light, far-red light, heat shock and the starvation state. Mutants defective in the pathway were isolated and three phenotypes obtained: blue-blind, general-blind and light-independent sporulating. When plasmodia of the blue-blind mutant Blu1 were exposed to a pulse of blue light and subsequently fused to non-induced wild-type plasmodia, the resulting heterokaryons sporulated, indicating a functional blue- light photoreceptor in the mutant. When the general-blind mutant Nos1 was fused to a wild-type plasmodium which had been induced by light, sporulation of the heterokaryon was blocked. However, the dominant inhibition of sporulation by Nos1 was gradually lost with increasing time between induction by light and time of fusion, suggesting that Nos1 can be bypassed by the time-dependent formation of a downstream signal-transduction intermediate. Phenotype expression in constitutively sporulating (Cos) mutants depended on starvation. The Cos2 product was titrated by fusing mutant plasmodia of different sizes to wild-type plasmodia of constant size and analysing the sporulation probability of the resulting heterokaryon. The titration curve indicates that a small change in the amount of Cos2 product can cause sporulation. We conclude that somatic complementation analysis allows the time-resolved evaluation of the regulatory function of mutations in a signal-transduction pathway without prior cloning of the gene. This shortcut allows us to characterize many mutants quickly and to select those for molecular analysis that display a well-defined regulatory function.

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Out of the blue; Phototropins of the leaf vascular bundle sheath mediate the blue light regulation of the leaf hydraulic conductance

10.1101/720912 ◽

2019 ◽

Author(s):

Yael Grunwald ◽

Sanbon Chaka Gosa ◽

Tanmayee Torne ◽

Nava Moran ◽

Menachem Moshelion

Keyword(s):

Signal Transduction ◽

Blue Light ◽

Vascular Bundle ◽

Vascular Tissue ◽

Xylem Sap ◽

Signal Transduction Pathway ◽

Hydraulic Conductance ◽

Bundle Sheath ◽

Transduction Pathway ◽

Water Permeability Coefficient

ABSTRACTThe leaf vascular bundle sheath cells (BSCs), which tightly envelop the leaf veins, constitute a selective dynamic barrier to water and solutes radially entering the mesophyll and play a major role in regulating the leaf radial hydraulic conductance (Kleaf). Recently, we showed that the BSCs’ plasma membrane H+-ATPase, AHA2, increases Kleaf by acidifying the xylem sap. Since BL reportedly increases Kleaf and we found the blue light (BL) receptor genes, PHOT1 and PHOT2 expressed in the Arabidopsis BSCs, we hypothesized that, similar to the guard cells (GCs) BL signal transduction pathway, the BSCs’ PHOT1 and PHOT2 activate the BSCs’ H+-ATPase and thus regulate Kleaf. Indeed, under BL illumination, the Kleaf in the knockout mutant lines phot1-5, phot2-1, phot1-5phot2-1 and aha2-4 was lower than in WT. BSCs-directed complementation (using the SCR promoter) of phot1-5 and aha2-4 respectively by PHOT1 and AHA2, restored the BL-induced Kleaf increase. BSCs-specific silencing of PHOT1 or PHOT2 (using the SCR promoter) abolished the BL-induced Kleaf increase. Xylem-fed PHOT inhibitor, tyrphostin 9, also abolished the BL-induced Kleaf increase in WT. Moreover, in WT plants, white light (WL) acidified the xylem sap compared to dark, but did not acidify the xylem sap of the phot1-5 mutant. BSCs-specific complementation of phot1-5 by SCR: PHOT1, restored the WL-induced xylem acidification. On a cellular level, BL hyperpolarized the BSCs, which was prevented by tyrphostin 9. In addition, the osmotic water permeability coefficient (Pf) of the BSCs was higher under WL treatment. Our results link the blue light control of water fluxes from the xylem to the mesophyll via the BSCs in the following model:BL →BSCs’ PHOTs activation →tyrosine phosphorylation→BSCs’ H+- ATPase activation →BSCs hyperpolarization, xylem acidification →Pf elevation → Kleaf increase. Thus, this study is the first to demonstrate an independent BL signal transduction pathway regulation of the vascular tissue.

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