*2.7. Transcriptome Analysis Revealed the Role of the RLCK VI\_A2 Kinase in Cellular Transport and Cell Wall Organisation*

High number of the *RLCK VI\_A2*-related DEGs code for proteins with catalytic, transport, transducer or binding activities, respectively (Table 1). Considering cellular localisation, proteins with extracellular (279, 23%) or cell periphery (395, 33%) localisation, and with association to cellular membranes (530, 44%), including the endomembrane system (118, 10%), were significantly overrepresented by the DEGs (Table 1 and Supplementary Tables S2 and S6). Moreover, 6% (72) of the DEGs are implicated in cell wall organisation and biogenesis (Supplementary Tables S2 and S6). Of note is the upregulation of several expansin and xyloglucan endotransglucosylase/hydrolase coding genes and the downregulation of those coding for extensin-like family proteins in the mutant background (Supplementary Table S6; for qRT-PCR validation Supplementary Figure S5c). Eight percent of DEGs (101) code for proteins that have transmembrane transport activities, including ion, nutrient or hormone transporters (Supplementary Table S6). Worth mentioning of the upregulation of several tonoplast intrinsic proteins and a number of auxin transporters, such as PIN4, PIN7, EIR1, ABCB19, LAX2, and the downregulation of many ion transporters (phosphate, sulphate, potassium etc.). These data indicate that RLCK VI\_A2-mediated protein phosphorylation is required for the proper cellular transport of a wide variety of ions, nutrients, structural and regulatory molecules.

#### **3. Discussion**

Plant growth and development have to be continuously harmonized with external conditions. Protein kinases have central roles in sensing environmental signals, as well as in coordinating cellular and developmental responses. Plants possess a large superfamily of diverse protein kinase types, including the signal-sensing transmembrane receptor kinases, RLKs, and various types of downstream intracellular signal-transducing kinases. Among the latter, receptor-like cytoplasmic kinases (RLCKs) have recently gained increasing interest as potential mediators and modulators of RLK signalling [4,32,33]. Nevertheless, only a few of the 149 Arabidopsis and 187 rice RLCKs have been characterized and have known functions. Here, we describe the characterization of a T-DNA insertion mutant of At*RLCK VI\_A2* that implies roles for the kinase in the regulation of cell/plant growth and morphogenesis.
