Two New Papers from Hake Lab

Rosa et al. The Maize MID-COMPLEMENTING ACTIVITY Homolog CELL NUMBER REGULATOR13/NARROW ODD DWARF Coordinates Organ Growth and Tissue Patterning. 
Organogenesis occurs through cell division, expansion, and differentiation. How these cellular processes are coordinated remains elusive. The maize (Zea mays) leaf provides a robust system to study cellular differentiation due to its distinct tissues and cell types. The narrow odd dwarf (nod) mutant displays defects at both the cellular and tissue level that increase in severity throughout growth. nod mutant leaves have reduced size due to fewer and smaller cells compared with the wild type. The juvenile-to-adult transition is delayed, and proximal distal-patterning is abnormal in this mutant. Differentiation of specialized cells such as those forming stomata and trichomes is incomplete. Analysis of nod-1 sectors suggests that NOD plays a cell-autonomous function in the leaf. We cloned nod positionally and found that it encodes CELL NUMBER REGULATOR13 (CNR13), the maize MID-COMPLEMENTING ACTIVITY homolog. CNR13/NOD is localized to the membrane and is enriched in dividing tissues. Transcriptome analysis of nod mutants revealed overrepresentation of cell wall, hormone metabolism, and defense gene categories. We propose that NOD coordinates cell activity in response to intrinsic and extrinsic cues.
Tsuda K. et al. KNOTTED1 cofactors, BLH12 and BLH14, regulate internode patterning and vein anastomosis in maize. 
Monocot stems lack the vascular cambium and instead have characteristic structures in which intercalary meristems generate internodes and veins remain separate and scattered. Developmental processes of these unique structures, however, have been poorly described. BELL1-like Homeobox (BLH) transcription factors (TFs) are known to heterodimerize with KNOTTED1-like Homeobox (KNOX) TFs to play crucial roles in shoot meristem maintenance, but their functions are elusive in monocots. We found that maize BLH12 and BLH14 have redundant but important roles in stem development. BLH12/14 interact with KNOTTED1 (KN1) in vivo, and accumulate in overlapping domains in shoot meristems, young stems and provascular bundles. Similar to kn1 loss-of-function mutants, blh12 blh14 (blh12/14) double mutants fail to maintain axillary meristems. Unique to blh12/14 is an abnormal tassel branching and precocious internode differentiation that results in dwarfism and reduced veins in stems. Micro-computed tomography (CT) observation of vascular networks revealed that blh12/14 double mutants had reduced vein number due to fewer intermediate veins in leaves and precocious anastomosis in young stems. Based on these results, we propose two functions of BLH12/14 during stem development: (1) maintaining intercalary meristems that accumulate KN1 and prevent precocious internode differentiation, (2) preventing precocious anastomosis of provascular bundles in young stems to ensure the production of sufficient independent veins.