MiR156-Targeted and Nontargeted SBP-Box Transcription Factors Act in Concert to Secure Male Fertility in Arabidopsis

Shuping Xing,Rita Berndtgen,Susanne Höhmann,María Salinas,Peter Huijser

doi:10.1105/tpc.110.079343

Shuping Xing, Rita Berndtgen + Show 3 more

Open Access

https://doi.org/10.1105/tpc.110.079343

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Abstract

The SBP-box transcription factor SQUAMOSA PROMOTER BINDING PROTEIN-LIKE8 (SPL8) is required for proper development of sporogenic tissues in Arabidopsis thaliana. Here, we show that the semisterile phenotype of SPL8 loss-of-function mutants is due to partial functional redundancy with several other members of the Arabidopsis SPL gene family. In contrast with SPL8, the transcripts of these latter SPL genes are all targeted by miR156/7. Whereas the introduction of single miR156/7-resistant SPL transgenes could only partially restore spl8 mutant fertility, constitutive overexpression of miR156 in an spl8 mutant background resulted in fully sterile plants. Histological analysis of the anthers of such sterile plants revealed an almost complete absence of sporogenous and anther wall tissue differentiation, a phenotype similar to that reported for sporocyteless/nozzle (spl/nzz) mutant anthers. Expression studies indicated a functional requirement for miR156/7-targeted SPL genes limited to early anther development. Accordingly, several miR156/7-encoding loci were found expressed in anther tissues at later stages of development. We conclude that fully fertile Arabidopsis flowers require the action of multiple miR156/7-targeted SPL genes in concert with SPL8. Either together with SPL/NZZ or independently, these SPL genes act to regulate genes mediating cell division, differentiation, and specification early in anther development. Furthermore, SPL8 in particular may be required to secure fertility of the very first flowers when floral transition-related miR156/7 levels might not have sufficiently declined.

Highlights

Flowering plants alternate during their life cycle between diploid sporophytic and haploid gametophytic generations
Using genetic approaches and histologic analyses, we demonstrated a clear role for SBP-box genes in early anther development
Note that a GUS signal appears in the pistils of pMIR156h:GUS flowers during late developmental stages ([A], arrows). (B) to (D), (F) to (H), and (J) to (L) Transverse sections of early, developing floral buds from 25-d-old plants after GUS staining

Summary

Introduction

Flowering plants alternate during their life cycle between diploid sporophytic and haploid gametophytic generations. Sexual reproduction requires a developmental phase transition resulting in the formation of flowers with highly specialized organs (i.e., anther-bearing stamen and ovule-bearing carpels). Within these organs, cells are recruited to undergo meiotic divisions to form male and female gametophytes. In Arabidopsis thaliana, the canonical homeotic ABC genes APETALA3, PISTILLATA, and AGAMOUS (AG) determine stamen identity of the third whorl floral organs. The latter is a direct activator of SPOROCYTELESS/NOZZLE (SPL/NZZ) more recently found to play a role in determining stamen identity (Ito et al, 2004; Liu et al, 2009). The postmeiotic stages 8 to 14 mainly consist of pollen maturation and anther structural adaptations for their release at anthesis

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