Phenotypic characterization of the CRISPA (ARP gene) mutant of pea (Pisum sativum; Fabaceae): a reevaluation.

Abstract

Leaf form and development are controlled genetically. The ARP genes encode MYB transcription factors that interact with Class 1 KNOX genes in a regulatory module that controls meristem-leaf determinations and is highly conserved in plants. ARP loss of function alleles and subsequent KNOX1 overexpression cause many unusual leaf phenotypes including loss or partial loss of the ability to produce a lamina and production of "knots" on leaf blades. CRISPA (CRI) is the ARP gene in pea, and a number of its mutant alleles are known. We made morphological and anatomical evaluations of cri-1 mutant plants while controlling for genetic background and for heteroblastic effects, and we used aldehyde fixation and resin preparations for anatomical analysis. Further, we compared gene expression in WT and cri-1 shoot tips and HOP1/PsKN1 and CRI expression in other leaf mutants. The cri-1 plants had more extensive abnormalities in the proximal than in the distal regions of the leaf, including ectopic stipules, narrow leaflets, and shortened petioles with excessive adaxial expansion. "Knots" were morphologically and anatomically variable but consisted of vascularized out-pocketing of the adaxial leaflet surface. HOP1/PsKN1 and UNI mRNA levels were higher in cri-1 shoot tips, and some auxin-regulated genes were lower. Low LE expression suggests that the GA level is high in cri-1 shoot tips. The CRISPA gene of pea suppresses KNOX1 genes and UNI and functions to (1) maintain proximal-distal regions in their appropriate positions, (2) restrict excessive adaxial cell proliferation, and (3) promote laminar expansion.