Two atypical ANGUSTIFOLIA without a plant‐specific C‐terminus regulate gametophore and sporophyte shapes in the moss Physcomitrium (Physcomitrella) patens.

Summary: ANGUSTIFOLIA (AN) is a plant‐specific subfamily of the CtBP/BARS/AN family, characterized by a plant‐specific C‐terminal domain of approximately 200 amino acids. Previously, we revealed that double knockout (DKO) lines of Physcomitrium (Physcomitrella) patensANGUSTIFOLIA genes (PpAN1‐1 and PpAN1‐2) show defects in gametophore height and the lengths of the seta and foot region of sporophytes, by reduced cell elongation. In addition to two canonical ANs, the genome of P. patens has two atypical ANs without a coding region for a plant‐specific C‐terminus (PpAN2‐1 and PpAN2‐2); these were investigated in this study. Similar to PpAN1s, both promoters of the PpAN2 genes were highly active in the stems of haploid gametophores and in the middle‐to‐basal region of young diploid sporophytes that develop into the seta and foot. Analyses of PpAN2‐1/2‐2 DKO and PpAN quadruple knockout (QKO) lines implied that these four AN genes have partially redundant functions to regulate cell elongation in their expression regions. Transgenic strains harboring P. patens α‐tubulin fused to green fluorescent protein, which were generated from a QKO line, showed that the orientation of the microtubules in the gametophore tips in the PpAN QKO lines was unchanged from the wild‐type and PpAN1‐1/1‐2 DKO plants. In addition to both PpAN2‐1 and PpAN2‐2, short Arabidopsis AN without the C‐terminus of 200 amino acids could rescue the Arabidopsis thaliana an‐1 phenotypes, implying AN activity is dependent on the N‐terminal regions. Significance Statement: ANGUSTIFOLIA (AN) regulates cell expansion in Arabidopsis thaliana and the moss Physcomitrium (Physcomitrella) patens. Analysis of two atypical paralogs of P. patens AN (PpAN2‐1 and PpAN2‐2) indicated that similar to two canonical PpAN1s, both PpAN2s have cell expansion functions in the gametophore stem and sporophyte seta and foot regions, and can recover the an‐1 mutant phenotypes of A. thaliana, although they have no plant‐specific C‐terminal regions of AN. [ABSTRACT FROM AUTHOR]