Role for Arabidopsis PLC7 in Stomatal Movement, Seed Mucilage Attachment, and Leaf Serration.

Ringo Van Wijk,Michel A Haring,Wilco Ligterink,Teun Munnik,Ana M Laxalt,Francisca Reyes Marquez,Qianqian Zhang,Xavier Zarza,Aisha Guardia,Mart Lamers,Denise Scuffi,Carlos García-Mata

doi:10.3389/fpls.2018.01721

Abstract

Phospholipase C (PLC) has been suggested to play important roles in plant stress and development. To increase our understanding of PLC signaling in plants, we have started to analyze knock-out (KO), knock-down (KD) and overexpression mutants of Arabidopsis thaliana, which contains nine PLCs. Earlier, we characterized PLC2, PLC3 and PLC5. Here, the role of PLC7 is functionally addressed. Promoter-GUS analyses revealed that PLC7 is specifically expressed in the phloem of roots, leaves and flowers, and is also present in trichomes and hydathodes. Two T-DNA insertion mutants were obtained, i.e., plc7-3 being a KO- and plc7-4 a KD line. In contrast to earlier characterized phloem-expressed PLC mutants, i.e., plc3 and plc5, no defects in primary- or lateral root development were found for plc7 mutants. Like plc3 mutants, they were less sensitive to ABA during stomatal closure. Double-knockout plc3 plc7 lines were lethal, but plc5 plc7 (plc5/7) double mutants were viable, and revealed several new phenotypes, not observed earlier in the single mutants. These include a defect in seed mucilage, enhanced leaf serration, and an increased tolerance to drought. Overexpression of PLC7 enhanced drought tolerance too, similar to what was earlier found for PLC3-and PLC5 overexpression. In vivo 32Pi-labeling of seedlings and treatment with sorbitol to mimic drought stress, revealed stronger PIP2 responses in both drought-tolerant plc5/7 and PLC7-OE mutants. Together, these results show novel functions for PLC in plant stress and development. Potential molecular mechanisms are discussed.

Highlights

In animals, phospholipase C (PLC) plays a key role in the perception and transmission of extracellular signals into cells
Histochemical GUS analyses on pPLC7-GUS-SYFP reporter lines indicated that PLC7 was mainly expressed in the vasculature throughout all stages of development, including root, cotyledons, leaves, hypocotyl, flower and silique septum (Figure 1), which is similar to the pattern of PLC3 (Zhang et al, 2018a) and PLC5 (Zhang et al, 2018b)
We demonstrated that Arabidopsis PLC3 and PLC5 were both involved in lateral root formation, but that the phenotype in a plc3/5-double mutant was not worse than the individual, single mutants

Summary

Introduction

Phospholipase C (PLC) plays a key role in the perception and transmission of extracellular signals into cells. Plants lack the primary targets for both IP3 and DAG, and have limited amounts of PIP2 in their membranes (van Leeuwen et al, 2007; Munnik and Nielsen, 2011; Munnik and Zarza, 2013; Munnik, 2014; Heilmann, 2016a,b; Gerth et al, 2017; Noack and Jaillais, 2017) They use phosphatidylinositol 4-phosphate (PIP) as an additional substrate and phosphorylate the resulting inositol phosphates and DAG into inositol polyphosphates (IPPs; e.g., IP6) and phosphatidic acid (PA), respectively, which can function as second messengers (Munnik, 2001; Gillaspy, 2013; Munnik, 2014; Heilmann, 2016a,b; Hou et al, 2016; Yao and Xue, 2018). PA is generated via PLC and DAG kinase (DGK); it can be formed via other DAG-generating enzymes, like non-specific PLCs (NPC), or directly, through phospholipase D (PLD) hydrolysis of structural phospholipids (Arisz et al, 2009; Munnik and Testerink, 2009; Pokotylo et al, 2013, 2018; Hou et al, 2016; Yao and Xue, 2018)

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Conclusion