Stems are important for plants to grow erectly. In stems, sclerenchyma cells must develop secondary cell walls to provide plants with physical support. To date, how sclerenchyma development is regulated remains largely unknown. In a recent study, Prof. YU Diqiu of Xishuangbanna Tropical Botanical Garden (XTBG) and his students provided evidence that that mutation of WRKY13 led to a weaker stem phenotype in A. thaliana, and WRKY13 was a positive regulator for overall stem development.

   In Arabidopsis thaliana, the WRKY transcription factor superfamily has 74 members with diverse functions. WRKY13 is a positive factor while WRKY12 is a negative one for lignin synthesis. Because the best A. thaliana protein match of WKRY12 is WKRY13, they hypothesized that plants evolved a pair of regulators from the same ancestor, which guaranteed proper development.

The study showed that sclerenchyma cell development was affected in wrky13 mutants. Firstly, the mutation of WRKY 13 caused weaker stem phenotype.  Secondly, close examination of inflorescence stem anatomy revealed that stem width, vascular bundle number and the percentage of sclerenchyma area were remarkably reduced in wrky13 mutants. Furthermore, examination of the lignin content level displayed that the lignin synthesis was repressed in WRKY 13 stems. In addition, the secondary cell wall synthesis gene NAC secondary wall thickening promoting factor 2 (NST2) was proved to be the direct downstream target of WRKY13.

The researchers thus proposed that WRKY13 affected the overall development of stem. It is possible that identification of the role of WRKY13 may help to resolve agricultural problems caused by weaker stems.

The study was financially supported by the Natural Science Foundation of China (U1202264and 31171183) and the Science Foundation of the Chinese Academy of Sciences (KSCX3-EW-N-07 and the CAS 135 program XTBG-F04).

 The study entitled “WRKY13 acts in stem development in Arabidopsis thaliana” has been published online in Plant Science.