Cooperative action of the paralogous maize lateral organ boundaries (LOB) domain proteins RTCS and RTCL in shoot‐borne root formation

Abstract

SummaryThe paralogous maize (Zea mays) LBD (Lateral Organ Boundaries Domain) genes rtcs (rootless concerning crown and seminal roots) and rtcl (rtcs-like) emerged from an ancient whole-genome duplication. RTCS is a key regulator of crown root initiation.The diversity of expression, molecular interaction and phenotype of rtcs and rtcl were investigated.The rtcs and rtcl genes display highly correlated spatio-temporal expression patterns in roots, despite the significantly higher expression of rtcs. Both RTCS and RTCL proteins bind to LBD downstream promoters and act as transcription factors. In line with its auxin inducibility and binding to auxin response elements of rtcs and rtcl promoters, ARF34 (AUXIN RESPONSE FACTOR 34) acts as transcriptional activator. Yeast two-hybrid screening combined with bimolecular fluorescence complementation (BiFC) experiments revealed conserved and unique interaction partners of RTCS and RTCL. The rtcl mutation leads to defective shootborne root elongation early in development. Cooperative action of RTCS and RTCL during shoot-borne root formation was demonstrated by rtcs-dependent repression of rtcl transcription in coleoptilar nodes.Although RTCS is instrumental in shoot-borne root initiation, RTCL controls shoot-borne root elongation early in development. Their conserved role in auxin signaling, but diverse function in shoot-borne root formation, is underscored by their conserved and unique interaction partners.

Non-syntenic genes drive RTCS-dependent regulation of the embryo transcriptome during formation of seminal root primordia in maize (Zea maysL.)

“…LBD proteins are essential in lateral organ initiation and patterning, and several members have been demonstrated to be involved in controlling different aspects of root development. For instance, LBD16, LBD18, LBD29, and LBD33 cooperatively regulate lateral root initiation and emergence in Arabidopsis (Okushima et al , 2007; Lee et al , 2009; Feng et al , 2012), RL1 is instrumental in lateral and shoot-borne root formation in rice (Inukai et al , 2005), and RTCS and its paralog RTCL regulate shoot-borne root initiation and elongation in maize (Xu et al , 2015). Differentially expressed genes associated with hormone functions between rtcs and wild-type embryos provide an opportunity to study RTCS-dependent regulation of auxin signaling and its interplay with other phytohormones during embryogenesis.…”

“…Seedlings at 10 d old were phenotyped and genotyped according to Xu et al (2015) to select homozygous rtcs and homozygous wild-type siblings. Subsequently, homozygous wild-type and mutant seedlings were transferred to soil pots in a growth chamber and grown under the same conditions as the paper rolls.…”

Use of genotype‐environment interactions to elucidate the pattern of maize root plasticity to nitrogen deficiency

“…Rtcs gene, which encodes a LOB domain protein, controls formation of embryonic seminal roots and the post‐embryonic shoot‐borne root systems (Taramino et al ). Rtcl is the paralog of Rtcs , cooperated with Rtcs , Rtcl controls shoot‐borne root elongation early in development (Xu et al ). Rum1 gene encodes a monocot specific AUX/IAA protein, controlling embryonic seminal roots and post‐embryonic lateral roots that initiated at the primary root (von Behrens et al ).…”

“…Rtcl is the paralog of Rtcs, cooperated with Rtcs, Rtcl controls shoot-borne root elongation early in development (Xu et al 2015). Rum1 gene encodes a monocot specific AUX/IAA protein, controlling embryonic seminal roots and post-embryonic lateral roots that initiated at the primary root (von Behrens et al 2011).…”

Genome-Wide Identification, Evolutionary Analysis and Expression Profiles of LATERAL ORGAN BOUNDARIES DOMAIN Gene Family in Lotus japonicus and Medicago truncatula

“…For instance, the maize Ramosa2 gene plays a role in regulation of inflorescence architecture [13]. Two maize LBD family genes RTCS and RTCL cooperatively act in shoot-borne root formation [14]. The rice auxin-inducible ARL1 gene encodes a LBD protein that promotes adventitious root formation [15].…”