Abstract
Core signaling pathways function in multiple programs during multicellular development. The mechanisms that compartmentalize pathway function or confer process specificity, however, remain largely unknown. In Arabidopsis thaliana, ERECTA (ER) family receptors have major roles in many growth and cell fate decisions. The ER family acts with receptor TOO MANY MOUTHS (TMM) and several ligands of the EPIDERMAL PATTERNING FACTOR LIKE (EPFL) family, which play distinct yet overlapping roles in patterning of epidermal stomata. Here, our examination of EPFL genes EPFL6/CHALLAH (CHAL), EPFL5/CHALLAH-LIKE1, and EPFL4/CHALLAH-LIKE2 (CLL2) reveals that this family may mediate additional ER-dependent processes. chal cll2 mutants display growth phenotypes characteristic of er mutants, and genetic interactions are consistent with CHAL family molecules acting as ER family ligands. We propose that different classes of EPFL genes regulate different aspects of ER family function and introduce a TMM-based discriminatory mechanism that permits simultaneous, yet compartmentalized and distinct, function of the ER family receptors in growth and epidermal patterning.
Highlights
The orchestration of programs that produce, pattern, and protect developing tissues is a complex regulatory problem
Because of this sequence similarity and functional similarities later revealed by our studies, it became useful to distinguish this subfamily of EPIDERMAL PATTERNING FACTOR LIKE (EPFL) as CHAL family (CHALf) ligands; we will refer to the CHAL paralogs as CHALLAH-LIKE1 (CLL1; EPFL5/ At3g22820) and CLL2 (EPFL4/At4g14723)
The structural similarities among the three CHALf members might lead to redundancy, such that a phenotype would be revealed only in multiple mutants; even in chal cll1 cll2 triple homozygotes, stomatal pattern appeared normal, and we observed no change in stomatal density (Figure 1F)
Summary
The orchestration of programs that produce, pattern, and protect developing tissues is a complex regulatory problem. Must individual cells execute complex genetic programs to obtain distinctive identities and morphologies, but they must do so in concert with their neighbors. Both plants and animals use peptide ligands and cell surface receptor-based signaling to establish cell fate and pattern and to regulate self-renewal. In plants, this signaling is often mediated by leucine-rich repeat, single transmembrane pass receptor-like kinases (LRR-RLKs; Shiu and Bleecker, 2001). The roles and receptor interactions of these putative ligands remain largely unknown, as do the mechanisms that enable related ligands to function in distinct processes and interact with different receptors
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