Cell type specific transcriptional reprogramming of maize leaves duringUstilago maydisinduced tumor formation

Abstract

34Ustilago maydis is a biotrophic pathogen and well-established genetic model to 35 understand the molecular basis of biotrophic interactions. U. maydis suppresses plant 36 defense and induces tumors on all aerial parts of its host plant maize. In a previous 37 study we found that U. maydis induced leaf tumor formation builds on two major 38 processes: the induction of hypertrophy in the mesophyll and the induction of cell 39 division (hyperplasia) in the bundle sheath. In this study we analyzed the cell-type 40 specific transcriptome of maize leaves 4 days post infection. This analysis allowed 41 identification of key features underlying the hypertrophic and hyperplasic cell identities 42 derived from mesophyll and bundle sheath cells, respectively. We examined the 43 differentially expressed (DE) genes with particular focus on maize cell cycle genes and 44found that three A-type cyclins, one B-, D-and T-type are upregulated in the 45 hyperplasic tumorous cells, in which the U. maydis effector protein See1 promotes cell 46 division. Additionally, most of the proteins involved in the formation of the pre-47replication complex (pre-RC, that assure that each daughter cell receives identic DNA 48 copies), the transcription factors E2Fand DPa as well as several D-type cyclins are 49 deregulated in the hypertrophic cells. 50 51Introduction 52 53Ustilago maydis is a biotrophic fungus that triggers tumors in all aerial parts of its host 54 plant maize (Zea mays). To attenuate activity of the maize immune system and colonize 55 the different maize organs, U. maydis deploys a set of proteins, so called effectors, 56which manipulate the plant cell metabolism, structure and function for its growth 57benefit. Such effectors are deployed in a time-, organ-and cell-type-specific manner to 58reprogram and/or cope with the different maize cell environments 1-11 . 59 60U. maydis infection induces characteristic symptoms that include chlorosis, which 61 appears 24 hours post infection (hpi), such lesions are produced in the absence of fungal 62 hyphae suggesting that they result from fungal products such as toxins or effectors 12 . 2 63 days post infection (dpi) anthocyanin streaking appears and fungal hyphae proliferate 64 and penetrate in between mesophyll cells. At 4 dpi the hyphae have reached the bundle 65 sheath cells and induce tumor formation while at 5 dpi small tumors are visible. 8 dpi 66 maize leaf cells are enlarged and fungal hyphae have undergone branching, a process 67 described as the beginning of teliospore formation 13,14 . Finally, at 12-14 dpi large 68 tumors are formed; inside such tumorous tissue hypha differentiate to give place to the 69 diploid teliospores 15 . Several studies have investigated maize transcriptional 70reprogramming in response to U. maydis infection 10,15-20 . On the cellular level, U. 71 maydis induced tumors in maize leaves were found to be constituted of hypertrophic 72 tumor (HTT) cells coming from transformed mesophyll cells (M), and hyperplasic 73 tumor (HPT) cells derived from b...

Roles of plant retinoblastoma protein: cell cycle and beyond

“…Irrespective of the whether infections impinge only on the RBR1 pathway or also other pathways, profound changes in the host cells are a primary outcome (Hanley‐Bowdoin et al , ; Ascencio‐Ibanez et al , ). Modulation of the RBR1 pathway is also seen with various other types of pathogens (Depuydt et al , ; Stes et al , ; Wen et al , ; Villajuana‐Bonequi et al , ). An unexpected link between the effector‐triggering immunity (ETI), and its associated programmed cell death, and the RBR1‐ERF module has been reported.…”

The functionally conserved effector Sta1 is a fungal cell wall protein required for virulence in Ustilago maydis

“…This could suggest that mutant hyphae, which lack Sta1 protein on the surface, might be recognized and elicit defense responses in this specific plant cell type. Transcriptional analysis in mesophyll cells and bundle sheath cells upon U. maydis infection demonstrated that the different plant cell type shows different gene expressions (Villajuana‐Bonequi et al , 2019), suggesting the possibility that specific plant cell types may show specific plant defense responses. In this scenario, Sta1 might protect hyphae or prevent release of cell wall fragments eliciting these defense responses.…”

Beyond What Your Retina Can See: Similarities of Retinoblastoma Function between Plants and Animals, from Developmental Processes to Epigenetic Regulation

“…In addition, ZmRBR3/4 transcripts accumulate in mitotic tissues from the endosperm. Recently, high levels of ZmRBR3/4 were found in tumor-like formations (induced by the fungus Ustilago maydis ) from maize leaves [ 118 , 123 ]. Interestingly, the protein complex ZmRBR3/4/E2F has a unique role not observed in other plants or animals: high levels of ZmRBR3/4 in complex with E2F promotes the expression of genes involved in DNA replication and cell cycle progression; contrary to what has been reported for overexpression of pRb and AtRBR ( Figure 2 C) [ 118 , 119 , 123 , 124 ].…”

“…Recently, high levels of ZmRBR3/4 were found in tumor-like formations (induced by the fungus Ustilago maydis ) from maize leaves [ 118 , 123 ]. Interestingly, the protein complex ZmRBR3/4/E2F has a unique role not observed in other plants or animals: high levels of ZmRBR3/4 in complex with E2F promotes the expression of genes involved in DNA replication and cell cycle progression; contrary to what has been reported for overexpression of pRb and AtRBR ( Figure 2 C) [ 118 , 119 , 123 , 124 ]. Besides, ZmRBR3/4 is negatively regulated by the ZmRBR1-E2F complex; as in lines expressing RepA, which inhibits ZmRBR1, ZmRBR3 is upregulated, suggesting a compensatory mechanism to ensure cell cycle progression [ 118 , 125 ].…”