Reconstruction of lateral root formation through single-cell RNA sequencing reveals order of tissue initiation

Pags 1362-1378 IlustracionesPostembryonic organogenesis is critical for plant development. Underground, lateral roots (LRs) form the bulk of mature root systems, yet the ontogeny of the LR primordium (LRP) is not clear. In this study, we performed the single-cell RNA sequencing through the first four stages of LR formation in Arabidopsis. Our analysis led to a model in which a single group of precursor cells, with a cell identity different from their pericycle origins, rapidly reprograms and splits into a mixed ground tissue/stem cell niche fate and a vascular precursor fate. The ground tissue and stem cell niche fates soon separate and a subset of more specialized vascular cells form sucrose transporting phloem cells that appear to connect to the primary root. We did not detect cells resembling epidermis or root cap, suggesting that outer tissues may form later, preceding LR emergence. At this stage, some remaining initial precursor cells form the primordium flanks, while the rest create a reservoir of pluripotent cells that are able to replace the LR if damaged. Laser ablation of the central and lateral LRP regions showed that remaining cells restart the sequence of tissue initiation to form a LR. Collectively, our study reveals an ontological hierarchy for LR formation with an early and sequential split of main root tissues and stem cells.This work was funded by the Ministerio de Economı´a y Competitividad (MINECO) of Spain and ERDF (grants BFU2016-80315-P and PID2019- 111523GB-I00 to M.A.M.-R), by the Comunidad de Madrid (CM) and Universidad Politécnica de Madrid (UPM; grant APOYO_JOVENES_ 2Y36R7_20_TRG6W7 [Plant_Stem] to P.P.-G.), the ‘‘Severo Ochoa (SO) Program for Centers of Excellence in R&D’’ from the Agencia Estatal de Investigacio´ n of Spain [SEV-2016-0672 (2017–2021)] to M.A.M.-R and P.P.-G via the CBGP, and by the National Institutes of Health (grant 1R35GM136362) and National Science Foundation (grant 1934388) to K.D.B. L.S.-R. and A.S.-C. were supported by FPI contracts (BES-2017- 080155 and BES-2014-068852, respectively) from MINECO, P.P.-G. by Programa Atraccion Talento from CM (2017-T2/BIO-3453) and SO, and J.C. by a Juan de la Cierva contract from MINECO (FJCI-2016-28607).Peer reviewe