The tapetum regulatory cascade for pollen coat lipid formation
Tapetum provides nutrition for microspore development, secrets
hydrolases for tetrad wall dissolution, and
supply
materials for pollen wall and pollen coat formation during anther
development. In Arabidopsis, the genetic regulatory pathway
DYT1-TDF1-AMS-MS188-MS1 is important for tapetum development and
function (Gu et al., 2014; Lou et al., 2014; Lou et al., 2018; Zhu et
al., 2011). In this pathway, AMS directly regulates ABCG26 for
sporopollenin transportation (J. Xu et al., 2010) and MGT5 to provide
the Mg2+ for microspores development (X. F. Xu et al.,
2015). MS188 directly regulates CYP703A2 and other sporopollenin
biosynthesis genes for sporopollenin synthesis and sexine formation (K.
Wang et al., 2018; Xiong et al., 2016). Sexine is the outer pollen wall
where pollen coat (including pollen coat lipids) are deposited. MS1 is a
transcription factor for late tapetum development directly regulated by
MS188. It regulates the expression of multiple pollen coat proteins (Lu
et al., 2020). MS1 also regulates the expression of KCS7 ,KCS15 and KCS21 for pollen coat lipid synthesis (Fig. 2,
5). This pollen coat lipid may provide a matrix for assembly of pollen
coat PCPs (Fig. 5b). After tapetum PCD, the endothecium-derived lipids
deposited outside of the pollen coat (Fig. 5b). Together, this work
reveals that following outer pollen wall formation regulated by MS188,
its directly regulating transcription factor MS1 regulates the
downstream gene expression for pollen coat formation. This regulatory
cascade is helpful to make sure that pollen wall and pollen coat are
orderly synthesized during anther development.