Expression Analysis of Mitogen-Activated Protein Kinases (MAPKs) Gene Family in Grapevine Berries

Research Article

Ann Agric Crop Sci. 2021; 6(8): 1103.

Expression Analysis of Mitogen-Activated Protein Kinases (MAPKs) Gene Family in Grapevine Berries

Hodaei A¹, Werbrouck S¹ and Çakir B²*

¹Laboratory for Applied In Vitro Plant Biotechnology, Department Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

²Department of Horticulture, Faculty of Agriculture, Ege University, Izmir, Turkey

*Corresponding author: Çakir B, Department of Horticulture, Faculty of Agriculture, Ege University, Bornova, Izmir 35100, Turkey

Received: November 17, 2021; Accepted: December 09, 2021; Published: December 16, 2021

Abstract

Plants, as sessile living organisms, are dependent on signalling mechanisms. Mitogen-activated protein kinases (MAPKs) are a highly conserved gene family that take a role in switching an extracellular signal into an intercellular signal. Ripening-related processes in non-climacteric fruits are not as well understood as in climacteric fruits. In this regard, studying MAPKs in grape berries during developmental stages may lead to a better understanding of physiological interactions during commercially relevant stages, such as pigmentation, ripening, and phenolics accumulation in the berries. Each MAPK cascade involves three or four MAPK proteins that facilitate signal transduction by phosphorylation of downstream targets. We examined the relative expression of VvMAP2Ks and VvMAP4Ks in berries at two-weekly intervals, from flowering to over-ripening. Expression analysis of 5 MAP2Ks and 7 MAP4Ks suggested that both gene families may play an active role in development of berries. Expression of VvMAP2K1 showed a correlation with abscisic acid (ABA) and ethylene accumulation. Moreover, the expression pattern of VvMAP2K2 and VvMAP2K3 shows a correlation with auxin, and ABA accumulation respectively. Furthermore, VvMAP2K4 may have a role in berry size increment and halting stomatal development. In addition, VvMAP2K5 may play a role in floral organ development. VvMAP4Ks expression pattern moves them forward to be excellent markers for monitoring the effect of for instance climate changerelated stress on berry development.

Keywords: Ripening; Veraison; Flowering; Fruit-set; Viticulture; Transcriptomics

Abbreviations

MAPK: MPK: Mitogen Activated Protein Kinase; MAP2K: MAPKK: MKK: Mitogen Activated Protein Kinase Kinase; MAP3K: MAPKKK: MKKK: Mitogen Activated Protein Kinase Kinase Kinase; MAP4K: MAPKKKK: MKKKK: Mitogen Activated Protein Kinase Kinase Kinase Kinase; SDS: Sodium Dodecyl Sulfate; PEG: Polyethylene Glycol; PVPP: Polyvinylpolypyrrolidone; ABA: Abscisic Acid; JA: Jasmonic Acid; BRs: Brassinosteroids; SIMK: Stress- Induced Mitogen-Activated Protein Kinase; SAMK: Stress-Activated Mitogen-Activated Protein Kinase; WIPK: Wound-Induced Mitogen-Activated Protein Kinase; HR: Hypersensitive Response; CTR: Constitutive Triple Response; NAA: Naphthaleneacetic Acid; DEPC: Diethyl Pyrocarbonate

Introduction

Grapevine is the most widely grown fruit crop in the world, covering approximately 7.454 million hectares in 2016 and producing more than 270 million hectoliters of wine [1]. The development of the grape berry, from fruit setting to overripening, is a complex process that requires a large number of events. Although the changes that occur as the berry begins to ripen have received considerable attention, their overall control and coordination remain poorly understood. Signalling regarding coordination is a crucial issue in berry development, as the changes that occur at both the physical and biochemical levels are considerable and rapid, occurring over only a few weeks.

According to Coombe [2], grape berry development is a dynamic process divided into three major phases. During Phase I, starting at fruit set, the diameter of the grape berry may double in size due to cell division and subsequent cell expansion, and organic acids, tannins, and hydroxycinnamates accumulate to peak levels. The second major phase (Phase II) is defined as a lag phase in which cell expansion ceases and berries remain firm. Sugars begin to accumulate and berries lose chlorophyll. The beginning of the third major phase (Phase III) is marked by ‘veraison’ as the onset of ripening in which berries undergo a second period of growth due to additional mesocarp cell expansion, accumulation of sugars, pigments, volatile compounds and a decline in organic acid accumulation.

The complexity of the molecular control during berry ripening has been exemplified by recent development in transcriptomics. Moreover, differential screening, cDNA, and oligonucleotide microarray analysis have shown that the expression of thousands of genes, including large numbers of transcription factors, do actually change during grape berry ripening [3-9].

Mitogen-activated protein kinases (MAPKs) represent a large group of proteins taking role in signal transduction within a cell. They consist of three or four MAPK proteins: MAPK, MAPK kinase (MAPKK = MAP2K), MAPK kinase kinase (MAPKKK = MAP3K), and MAPK kinase kinase kinase (MAPKKKK = MAP4K). The MAPK pathway plays an important role in the conversion of an extracellular signal into an intercellular one through protein phosphorylation. MAPK proteins sequentially activate each other by phosphorylation. In other words, MAPKs form signalling modules where MAPK kinase kinases (MAPKKKs) activate MAPK kinases (MAPKKs) which in turn activate MAPKs. Activated MAPK can trigger a pathway or activate a transcription factor [10,11]. In addition to this, MAPK proteins have the potential to crosstalk with other pathways or can act as a negative regulator [12]. For instance, CTR1, which is a MAPKKK, is known as a negative regulator of ethylene signalling [13]. They are highly conserved in eukaryotes including yeast, animals, and plants where they are involved in cytokinesis, differentiation, proliferation, hormonal responses; abiotic and biotic stress signalling and developmental programs [10,14-16].

Expression analysis of MAPK genes during berry developmental stages can create an understanding of both primary and secondary metabolisms during berry ripening. To our knowledge, this is the first report about the expression of VvMAP2Ks and VvMAP4Ks during grape berry development. These markers may lead us to a better understanding of signalling processes specifically, and grape berry development physiology in general.

Materials and Methods

Plant tissue

Seedless grapes, Vitis vinifera ‘Sultana’ berries were used for analysis. Berries were collected every two weeks from fruit set (26.05) until full ripening (17.09) from an 8-years-old vineyard located at the Ege University Agricultural Experiment Station, Izmir, Ege, Turkey. Berries were sampled from different blocks, immediately frozen and ground in liquid nitrogen to be stored at -80°C.

RNA extraction

Total RNA from grape berries of the variety Sultana was extracted according to Davies and Robinson [17], with an additional step of selective precipitation with 2 M LiCl. The extraction buffer contained 0.3 M Tris, 5 M Sodium perchlorate monohydrate (ClH2NaO5), 1% SDS, 2% PEG, 8.5% PVPP, and just prior to use, 1% Β-mercaptoethanol. Two grams of ground powder was added to a pre-warmed (30-35°C) extraction buffer at 5ml/g of tissue and shaken at 37°C for 90 minutes at 180 × rpm. Vacuum filtration was done before adding 96% alcohol and was kept overnight at -20°C.

On the second day, samples were centrifuged at 4°C for 30 minutes at 5000 × rpm. 2ml of 70% alcohol was added prior to centrifugation at 4°C for 5 minutes at 5000 × rpm. The precipitate was dissolved in DEPC water, and mixtures were extracted twice with equal volumes of phenol:chloroform:isoamyl alcohol (25:24:1, v/v) then centrifuged at 10,000 × rpm for 7 minutes at 4°C. Chloroform:isoamyl alcohol (24:1, v/v) was added to the supernatant before a centrifuge at 10,000 × rpm for 7 minutes at 4°C. Ten % (V/V) of 3 M NaOAc (pH 5.2) was added to the supernatant, mixed, and then stored at -80°C for 90 minutes. Total RNA pellets were collected by centrifugation at 10,000 × rpm for 20 minutes at 4°C. Each pellet was dissolved in 200μl of DEPC water prior to adding 100μl of 10 M LiCl as the last step of the second day and this was stored at 4°C for 16-20 hours. On the third and the last day, pellets were collected by centrifugation at 10,000 × rpm for 40 minutes at 4°C, 500μl of 70% alcohol was added to the pellet prior to centrifugation at 10,000 × rpm for 5 minutes at 4°C. The pellet was dissolved in 30μl of DEPC water and was stored at -20°C.

Quantitative real-time PCR (qRT-PCR)

The expression of MAPK genes in grape berries were confirmed by qRT-PCR analysis. Total RNA was extracted from samples as above and treated with DNase I (Fermentas, USA). First-strand cDNA was performed by using the Transcriptor First Strand cDNA Synthesis Kit (Roche, Switzerland) according to the manufacturer’s protocol.

Çakir and Kiliçkaya [18] revealed the existence of 14 MAPKs, 5 MAP2Ks, 62 MAP3Ks, and 7 MAP4Ks in Vitis vinifera, which were used as primer data information. VvActin was used as a housekeeping gene in regard to normalization and elimination of pipetting errors [19].

Primers used are listed in Table 1. LightCycler® FastStart DNA Master SYBR Green I Kit (Roche, Switzerland) was utilized for preparation of qRT-PCR reactions and reactions were run by using Roche LightCycler 480. Three replicates were conducted to analyze the expression of each gene under each condition. The 2-ΔΔCT method was used for calculation of relative expression levels [20]. Transcript abundance was normalized to that of Vvactin.