The Arabidopsis CALLOSE DEFECTIVE MICROSPORE1 Gene Is Required for Male Fertility through Regulating Callose Metabolism during Microsporogenesis

Abstract

ORCID IDs: 0000-0002-3941-9955 (P.L.); 0000-0001-8717-4422 (H.M.).During angiosperm microsporogenesis, callose serves as a temporary wall to separate microsporocytes and newly formed microspores in the tetrad. Abnormal callose deposition and dissolution can lead to degeneration of developing microspores. However, genes and their regulation in callose metabolism during microsporogenesis still remain largely unclear. Here, we demonstrated that the Arabidopsis (Arabidopsis thaliana) CALLOSE DEFECTIVE MICROSPORE1 (CDM1) gene, encoding a tandem CCCH-type zinc finger protein, plays an important role in regulation of callose metabolism in male meiocytes and in integrity of newly formed microspores. First, quantitative reverse transcription PCR and in situ hybridization analyses showed that the CDM1 gene was highly expressed in meiocytes and the tapetum from anther stages 4 to 7. In addition, a transfer DNA insertional cdm1 mutant was completely male sterile. Moreover, light microscopy of anther sections revealed that microspores in the mutant anther were initiated, and then degenerated soon afterward with callose deposition defects, eventually leading to male sterility. Furthermore, transmission electron microscopy demonstrated that pollen exine formation was severely affected in the cdm1 mutant. Finally, we found that the cdm1 mutation affected the expression of callose synthesis genes (CALLOSE SYNTHASE5 and CALLOSE SYNTHASE12) and potential callase-related genes (A6 and MYB80), as well as three other putative b-1,3-glucanase genes. Therefore, we propose that the CDM1 gene regulates callose metabolism during microsporogenesis, thereby promoting Arabidopsis male fertility.

AtC3H14, a plant‐specific tandem CCCH zinc‐finger protein, binds to its target mRNAs in a sequence‐specific manner and affects cell elongation in Arabidopsis thaliana

“…First, AtC3H14 is a direct target of MYB46, a master switch for secondary wall biosynthesis, and was able to activate in vitro all of the eight secondary wall biosynthesis genes tested in a trans‐activation assay (Ko et al ., ; Kim et al ., ); Second, AtC3H14 and its homologs (e.g., AtC3H15 and PtC3H17 ) are predominantly expressed in secondary wall‐forming tissues (Figures , S1 and S2) and co‐expressed with MYB46 (Figure S3). Recently, it has been suggested that AtC3H15 may regulate callose metabolism during microsporogenesis (Lu et al ., ); Third, the transgenic plants overexpressing AtC3H14 ( 35S::AtC3H14 ) showed early and aberrant phloem fiber development both in the stems and roots (Figure ). Fourth, these phenotypes are consistently reproduced in the transgenic plants overexpressing its Arabidopsis ( 35S::AtC3H15 ) and poplar homolog ( 35S::PtC3H17 ) (Figure S6).…”

Genetic and Biochemical Mechanisms of Pollen Wall Development

“…CALLOSE DEFECTIVE MICROSPORE 1 (CDM1), acts on callose biosynthetic and degrading genes [90], while AtTTP (TRISTETRAPROLINE) forms a genetic pathway including AtTTPmiR160-ARF17-CalS5 [91]. Furthermore, AtbZIP34 was shown to modulate pollen wall development by targeting six genes associated with lipid metabolism and/or transport, including AtABCB9 [92].…”

Anther and pollen development: A conserved developmental pathway

“…After meiosis, the tapetum secretes b1,3 glucanase (callase), which breaks down the callose layer surrounding the tetrads and releasing the microspores into the locule (Lu et al 2014). The timing of callase secretion appears critical for pollen development (Bedinger 1992), with miss-expression causing sterility (Worrall et al 1992).…”