Regulation of unipinnate character in the distal tendrilled domain of compound leaf-blade by the gene MULTIFOLIATE PINNA (MFP) in pea Pisum sativum

Abstract

The wild type compound leaf-blade of Pisum sativum has one to three pairs of simple leaflet pinnae in its petiole proximal domain, one to four pairs of simple tendril pinnae in the distal domain and a simple tendril pinna in the apical domain. A novel ethyl methane sulfonate induced dominant mutant was isolated and characterized whose leaf-blades formed MULTIFOLIATE PINNA pairs in the distal domain. The distal multifoliate pinnae or compound pinna-blades had three tendrilled-leaflets as pinnules. The pinnules had a bifacial elliptic-lanceolate leaflet body and arc shaped apex that mimicked the ringlet shaped apex of tendrils. The TL/tl, mfp/mfp and tl/tl, mfp/mfp leaf-blades also produced multifoliate (compound) pinna-blades in distal positions; the pinnules of these genotypes had elliptic shape. The pinnae were branched tendrils in TL/TL, MFP/mfp plants. The leaf-blade rachis was more ramified in af mfp double mutants than in af mutant. In the af mfp double mutant, the multifoliate pinna-blades were present on tertiary and secondary branches of the rachis in the proximal domain and on secondary branches and the primary rachis in the distal domain. The leaf-blades of the af tl mfp triple mutant genotype were an order of magnitude more ramified than those of af tl and af mfp genotypes in proximal as well as distal domains. The leaf-blade phenotypes of various genotypes revealed in this study and those known from previous work have allowed the following conclusions about the nature of mfp mutation and mfp function(s). (a) The presence of mfp mutation or mfp function changes the identity of distal primordia, from tendrils in the wildtype (MFP/MFP) leaf-blades to multifoliate pinna-blades in mfp/mfp mutant. (b) A pathway for the lamination of pinnules of multifoliate blades formed in distal and terminal domains in the mfp mutant and all domains in af mfp double mutant is activated by the mfp mutation. (c) The leaflet-/pinnule-lamination pathway activated by the tl mutation interacts with the mfp-directed pathway. (d) The mfp mutation intensifies rachis ramification in proximal and distal domains activated by the af mutation. This process is distinct from analogous rachis ramification that occurs in the af tl double mutant.