Biphasic regulation of the transcription factor ABORTED MICROSPORES (AMS) is essential for tapetum and pollen development in Arabidopsis

Abstract

Summary Viable pollen is essential for plant reproduction and crop yield. Its production requires coordinated expression at specific stages during anther development, involving early meiosis‐associated events and late pollen wall formation. The ABORTED MICROSPORES (AMS) transcription factor is a master regulator of sporopollenin biosynthesis, secretion and pollen wall formation in Arabidopsis. Here we show that it has complex regulation and additional essential roles earlier in pollen formation.An inducible‐AMS reporter was created for functional rescue, protein expression pattern analysis, and to distinguish between direct and indirect targets. Mathematical modelling was used to create regulatory networks based on wild‐type RNA and protein expression.Dual activity of AMS was defined by biphasic protein expression in anther tapetal cells, with an initial peak around pollen meiosis and then later during pollen wall development. Direct AMS‐regulated targets exhibit temporal regulation, indicating that additional factors are associated with their regulation.We demonstrate that AMS biphasic expression is essential for pollen development, and defines distinct functional activities during early and late pollen development. Mathematical modelling suggests that AMS may competitively form a protein complex with other tapetum‐expressed transcription factors, and that biphasic regulation is due to repression of upstream regulators and promotion of AMS protein degradation.

Positive regulation of AMS by TDF1 and the formation of a TDF1–AMS complex are required for anther development in Arabidopsis thaliana

“…Previous studies have shown that TDF1 alone is sufficient to activate the expression of genes required for pollen wall synthesis (Gu et al ., ), suggesting that DYT1–TDF1–AMS can maintain normal pollen wall formation via TDF1 regulation after DYT1 decreases, which is supported by the short‐term expression of the DYT1‐GFP protein in the tapetum (Gu et al ., ). The FFL of TDF1–AMS–MS188 may prolong the time during which MS188 is transcribed, which is consistent with the two peaks of the MS188 expression pattern in stages 6–8, during which the second peak of MS188 is higher than the first peak (Ferguson et al ., ).…”

“…Bars, 20 lm. Considering that the expression of direct AMS targets that are responsible for tapetum development and pollen wall formation are required as additional factors for activation, regardless of the functional AMS presence (Ferguson et al, 2017), we speculated that TDF1 and AMS are involved in this downstream transcription network by forming heterodimers. To find out if TDF1 has the ability to bind to targets of AMS, we assayed the enrichments of the MS188 and TEK genes in the tdf1 À/À gpTDF1:TDF1-GFP lines via a ChIP analysis.…”

Cytological and Transcriptomic Analyses Reveal Important Roles of CLE19 in Pollen Exine Formation

“…AMS is a key regulator of sporopollenin biosynthesis, secretion, and pollen wall formation and can form a complex with MS188/MYB103/ MYB80 that likely activates the expression of CYP703A2 and MS1 encoding a transcription factor (Xu et al, 2010Zhu et al, 2011;Feng et al, 2012;Gu et al, 2014;Xiong et al, 2016;Ferguson et al, 2017). DYT1 and MYB35/TDF1 are required for the development of tapetum and reproductive cells at early stages, as supported by the findings that DYT1 and MYB35/TDF1 mutants exhibit abnormal tapetal cells at anther stage 5 and onward and that their anthers lack any pollen (Zhang et al, 2006;Zhu et al, 2008;Gu et al, 2014).…”

Auxin export from proximal fruits drives arrest in competent inflorescence meristems

“…We firstly tested whether exogenous application of auxin to fruits of an infertile mutant could re-initiate the timely arrest of the PI. We treated sterile fruit in the ams mutant, which like ms1 fails to go through normal floral arrest [12], with the auxin analog NAA from 6 dpa. This resulted in earlier IM arrest with the PI producing ~50 fruit, compared to ~80 in mock-treated plants (Fig.…”

“…Arabidopsis wild-types Col-0 and Ler were used as indicated. The following lines have previously been described before; ms1-1 (Ler background) [14]; AMS:AMS-GR ams (Col-0 background, ams is SALK_152147) [12]; MS1:MS1-GR ms1-1 (Ler background) [15].…”