Phloem parenchyma (PP) cells of Arabidopsis leaf veins trans-differentiate to become PP transfer cells (TCs) which are thought to aid phloem loading by facilitating unloading of photoassimilates into the apoplasm for subsequent energy-dependent uptake into the sieve element/companion cell complex. We are using PP TCs in Arabidopsis as a genetic model to identify transcription factors involved in coordinating the deposition of the wall ingrowth network. Experimental approaches include bioinformatics analysis of temporal and spatial development of wall ingrowth deposition in Arabidopsis cotyledons and leaves using data public microarray data and our own RNA-Seq experiments. A cohort of transcription factors were identified as commonly up-regulated across the experimental comparisons surveyed in both analyses, with a uniquely high representation of NAC-domain genes. Selected NACs chosen based on their expression characteristics and phylogenetic relationships have been phenotypically tested for disrupted PP TC development in corresponding mutants, along with compromised sucrose-dependent root growth possibly due to an impaired capacity for phloem loading. The outcomes from these experiments suggest the involvement of NAC056 and NAC018 in regulating wall ingrowth deposition of Arabidopsis PP TCs, with NAC056 found to be specifically expressed in PP TCs as reported by a leaf vasculature single-cell transcriptome from another lab. We are currently refining the sensitivity and accuracy of transcript profiling, and our attempt of sampling vascular-enriched tissue obtained by isolation of intact vascular bundles and single-cell sequencing will be reported.