Influence of Switchgrass TDIF-like Genes on Arabidopsis Vascular Development

As a member of the CLAVATA3 (CLV3)/EMBRYO SURROUNDING REGION (CLE) family, the dodecapeptide tracheary element differentiation inhibitory factor (TDIF) has a major impact on vascular development in plants. However, the influence of polymorphisms in the TDIF peptide motif on activity remains poorly understood. The model plant, Arabidopsis provides a fast and effective tool for assaying the activity of TDIF homologs. Five TDIF homologs from a group of 93 CLE genes in switchgrass (Panicum virgatum), a perennial biomass crop, named PvTDIF-like (PvTDIFL) genes were studied. The expression levels of PvTDIFL1, PvTDIFL3MR3, and PvTDIFL3MR2 were relatively high and all of them were expressed at the highest levels in the rachis of switchgrass. The precursor proteins for PvTDIFL1, PvTDIFL3MR3, and PvTDIFL3MR2 contained one, three, and two TDIFL motifs, respectively. Treatments with exogenous PvTDIFL peptides increased the number of stele cells in the hypocotyls of Arabidopsis seedlings, with the exception of PvTDIFL_4p. Heterologous expression of PvTDIFL1 in Arabidopsis strongly inhibited plant growth, increased cell division in the vascular tissue of the hypocotyl, and disrupted the cellular organization of the hypocotyl. Although heterologous expression of PvTDIFL3MR3 and PvTDIFL3MR2 also affected plant growth and vascular development, PvTDIFL activity was not enhanced by the multiple TDIFL motifs encoded by PvTDIFL3MR3 and PvTDIFL3MR2. These data indicate that in general, PvTDIFLs are functionally similar to Arabidopsis TDIF but that the processing and activities of the PvTDIFL peptides are more complex.

An auxin transport network underlies xylem bridge formation between the hemi-parasitic plant Phtheirospermum japonicum and host Arabidopsis

ABSTRACTParasitic plants form vascular connections with host plants for efficient material transport. The haustorium is the responsible organ for host invasion and subsequent vascular connection. After invasion of host tissues, vascular meristem-like cells emerge in the central region of the haustorium, differentiate into tracheary elements and establish a connection, known as a xylem bridge, between parasite and host xylem systems. Despite the importance of this parasitic connection, the regulatory mechanisms of xylem bridge formation are unknown. Here, we show the role of auxin and auxin transporters during the process of xylem bridge formation using an Orobanchaceae hemiparasitic plant, Phtheirospermum japonicum. The auxin response marker DR5 has a similar expression pattern to tracheary element differentiation genes in haustoria. Auxin transport inhibitors alter tracheary element differentiation in haustoria, but biosynthesis inhibitors do not, demonstrating the importance of auxin transport during xylem bridge formation. The expression patterns and subcellular localization of PIN family auxin efflux carriers and AUX1/LAX influx carriers correlate with DR5 expression patterns. The cooperative action of auxin transporters is therefore responsible for controlling xylem vessel connections between parasite and host.

Active DNA demethylation regulates tracheary element differentiation in Arabidopsis

DNA demethylation is important for the erasure of DNA methylation. The role of DNA demethylation in plant development remains poorly understood. Here, we found extensive DNA demethylation in the CHH context around pericentromeric regions and DNA demethylation in the CG, CHG, and CHH contexts at discrete genomic regions during ectopic xylem tracheary element (TE) differentiation. While loss of pericentromeric methylation occurs passively, DNA demethylation at a subset of regions relies on active DNA demethylation initiated by DNA glycosylases ROS1, DML2, and DML3. The ros1 and rdd mutations impair ectopic TE differentiation and xylem development in the young roots of Arabidopsis seedlings. Active DNA demethylation targets and regulates many genes for TE differentiation. The defect of xylem development in rdd is proposed to be caused by dysregulation of multiple genes. Our study identifies a role of active DNA demethylation in vascular development and reveals an epigenetic mechanism for TE differentiation.

Auxin transport network underlies xylem bridge formation between the hemi-parasitic plant Phtheirospermum japonicum and host Arabidopsis

ABSTRACTParasitic plants form vascular connections to host plants for efficient material transport. The haustorium is the responsible organ for host invasion and subsequent vascular connection. After invasion of host tissues, vascular meristem-like cells emerge in the central region of the haustorium, differentiate into tracheary elements, and establish a connection, known as a xylem bridge, between parasite and host xylem systems. Despite the importance of this parasitic connection, the regulatory mechanisms of xylem bridge formation are unknown. Here we show the role of auxin and auxin transporters during the process of xylem bridge formation using an Orobanchaceae hemiparasitic plant, Phtheirospermum japonicum. The auxin response marker DR5 has a similar expression pattern to tracheary element differentiation genes in haustoria. Auxin transport inhibitors alter tracheary element differentiation in haustoria, but biosynthesis inhibitors do not, demonstrating the importance of auxin transport during xylem bridge formation. The expression patterns and subcellular localization of PIN family auxin efflux carriers and AUX/LAX influx carriers correlate with DR5 expression patterns. The cooperative action of auxin transporters is therefore responsible for controlling xylem vessel connections between parasite and host.

РОЛЬ ПЕПТИДА CLE 41 В РАЗВИТИИ ЗАПАСАЮЩЕЙ ПАРЕНХИМЫ КОРНЯ У ПРЕДСТАВИТЕЛЕЙ РОДА RAPHANUS L., "Физиология растений"

CLE-пептиды (CLAVATA3/ENOSPERM SURROUNDING REGION) - сигнальные молекулы-фитогормоны, которые играют центральную роль в контроле развития разных типов меристем, регулируя экспрессию генов WOX (WUSCHEL-RELATED HOMEOBOX). В частности, мишенями действия CLE-пептидов небольшой группы TDIF (Tracheary Element Differentiation Inhibitory Factor) является ген WOX4 - центральный регулятор развития камбия и проводящей системы. Мы изучали роль пептида группы TDIF CLE 41 в развитии запасающего корня на представителях рода Raphanus: культурном редисе (Raphanus sativus) - популярной корнеплодной культуре с запасающим корнем и его дикорастущем предке редьке полевой (Raphanus raphanistrum), у которой запасающая паренхима корня развита слабо. Было показано влияние сверхэкспрессии гена RsCLE 41 и обработки растений экзогенным пептидом CLE 41 на развитие камбия и ксилемы в корнях R. sativus и R. raphanistrum, а также на экспрессию генов разных групп. В целом можно сказать, что CLE 41 активирует экспрессию генов, гомологи которых у арабидопсиса играют центральную роль в поддержании камбия (RsWOX4, RsWOX14, RsHAM4, RsCYCD 3). В запасающем корне редиса пептид CLE 41 активирует пролиферацию клеток камбия, при этом снижая количество одного из элементов ксилемы - одревесневшей паренхимы. Полученные данные свидетельствуют о важной роли CLE 41 в развитии запасающего корня редиса.