Mutational Analysis of Branching in Pea. Evidence ThatRms1 and Rms5 Regulate the Same Novel Signal

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Abstract
The fifth increased branching ramosus(rms) mutant, rms5, from pea (Pisum sativum), is described here for phenotype and grafting responses with four other rms mutants. Xylem sap zeatin riboside concentration and shoot auxin levels inrms5 plants have also been compared withrms1 and wild type (WT). Rms1 andRms5 appear to act closely at the biochemical or cellular level to control branching, because branching was inhibited in reciprocal epicotyl grafts between rms5 orrms1 and WT plants, but not inhibited in reciprocal grafts between rms5 and rms1 seedlings. The weakly transgressive or slightly additive phenotype of therms1 rms5 double mutant provides further evidence for this interaction. Like rms1, rms5rootstocks have reduced xylem sap cytokinin concentrations, andrms5 shoots do not appear deficient in indole-3-acetic acid or 4-chloroindole-3-acetic acid. Rms1 andRms5 are similar in their interaction with otherRms genes. Reciprocal grafting studies withrms1, rms2, and rms5, together with the fact that root xylem sap cytokinin concentrations are reduced in rms1 and rms5 and elevated inrms2 plants, indicates that Rms1 andRms5 may control a different pathway than that controlled by Rms2. Our studies indicate thatRms1 and Rms5 may regulate a novel graft-transmissible signal involved in the control of branching.