RT Journal Article
SR Electronic
T1 Out of the blue; Phototropins of the leaf vascular bundle sheath mediate the blue light regulation of the leaf hydraulic conductance
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 720912
DO 10.1101/720912
A1 Yael Grunwald
A1 Sanbon Chaka Gosa
A1 Tanmayee Torne
A1 Nava Moran
A1 Menachem Moshelion
YR 2020
UL http://biorxiv.org/content/early/2020/10/21/720912.abstract
AB The 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.Competing Interest StatementThe authors have declared no competing interest.