Mutations inNAKED-ENDOSPERMIDD genes reveal functional interactions withSCARECROWand a maternal influence on leaf patterning in C₄grasses

Abstract

Leaves comprise a number of different cell-types that are patterned in the context of either the epidermal or inner cell layers. In grass leaves, two distinct anatomies develop in the inner leaf tissues depending on whether the leaf carries out C3 or C4 photosynthesis. In both cases a series of parallel veins develops that extends from the leaf base to the tip but in ancestral C3 species veins are separated by a greater number of intervening mesophyll cells than in derived C4 species. We have previously demonstrated that the GRAS transcription factor SCARECROW (SCR) regulates the number of photosynthetic mesophyll cells that form between veins in the leaves of the C4 species maize, whereas it regulates the formation of stomata in the epidermal leaf layer in the C3 species rice. Here we show that SCR is required for inner leaf patterning in the C4 species Setaria viridis but in this species the presumed ancestral stomatal patterning role is also retained. Through a comparative mutant analysis between maize, setaria and rice we further demonstrate that loss of NAKED-ENDOSPERM (NKD) INDETERMINATE DOMAIN (IDD) protein function exacerbates loss of function scr phenotypes in the inner leaf tissues of maize and setaria but not rice. Specifically, in both setaria and maize, scr;nkd mutants exhibit an increased proportion of fused veins with no intervening mesophyll cells. Thus, combined action of SCR and NKD may control how many mesophyll cells are specified between veins in the leaves of C4 but not C3 grasses. Finally, we identified a maternal effect in maize whereby maternally derived NKD can affect patterning of cells in leaf primordia that are initiated during embryogenesis. Together our results provide insight into the evolution of cell patterning in grass leaves, demonstrate a novel patterning role for IDD genes in C4 leaves and suggest that NKD can influence embryonic leaf development non-cell autonomously from the surrounding maternal tissue.

Properties of INDETERMINATE DOMAIN Proteins from Physcomitrium patens: DNA-Binding, Interaction with GRAS Proteins, and Transcriptional Activity

“…IDD proteins from Arabidopsis , rice, and other plants could interact with GRAS proteins, such as DELLA and SHR [ 14 , 15 , 17 , 21 , 22 , 47 , 48 ]. We examined whether PpIDD proteins interact with GRAS proteins from P. patens and Arabidopsis by using a Y2H assay.…”

“…IDD proteins from Arabidopsis, rice, and other plants could interact with GRA teins, such as DELLA and SHR [14,15,17,21,22,47,48]. We examined whether PpID teins interact with GRAS proteins from P. patens and Arabidopsis by using a Y2H as P. patens, two DELLA genes and two SHR genes were identified [7,8,40,49], and cD PpDELLAa and PpDELLAb and one for PpSHR (PpSHR2) were obtained.…”